diff --git a/modules/openapi-generator/src/main/resources/csharp/api.mustache b/modules/openapi-generator/src/main/resources/csharp/api.mustache
index 63fdd07f19b..d7e0571ef60 100644
--- a/modules/openapi-generator/src/main/resources/csharp/api.mustache
+++ b/modules/openapi-generator/src/main/resources/csharp/api.mustache
@@ -397,7 +397,7 @@ namespace {{packageName}}.{{apiPackage}}
                 {{/isArray}}
                 {{/isFile}}
                 {{^isFile}}
-                localVarRequestOptions.FormParameters.Add("{{baseName}}", {{packageName}}.Client.ClientUtils.ParameterToString({{paramName}})); // form parameter
+                localVarRequestOptions.FormParameters.Add("{{baseName}}", {{packageName}}.Client.ClientUtils.{{#isPrimitiveType}}ParameterToString{{/isPrimitiveType}}{{^isPrimitiveType}}Serialize{{/isPrimitiveType}}({{paramName}})); // form parameter
                 {{/isFile}}
             }
             {{/required}}
@@ -647,7 +647,7 @@ namespace {{packageName}}.{{apiPackage}}
             {{/isArray}}
             {{/isFile}}
             {{^isFile}}
-            localVarRequestOptions.FormParameters.Add("{{baseName}}", {{packageName}}.Client.ClientUtils.ParameterToString({{paramName}})); // form parameter
+            localVarRequestOptions.FormParameters.Add("{{baseName}}", {{packageName}}.Client.ClientUtils.{{#isPrimitiveType}}ParameterToString{{/isPrimitiveType}}{{^isPrimitiveType}}Serialize{{/isPrimitiveType}}({{paramName}})); // form parameter
             {{/isFile}}
             {{/required}}
             {{^required}}
@@ -669,7 +669,7 @@ namespace {{packageName}}.{{apiPackage}}
                 {{/isArray}}
                 {{/isFile}}
                 {{^isFile}}
-                localVarRequestOptions.FormParameters.Add("{{baseName}}", {{packageName}}.Client.ClientUtils.ParameterToString({{paramName}})); // form parameter
+                localVarRequestOptions.FormParameters.Add("{{baseName}}", {{packageName}}.Client.ClientUtils.{{#isPrimitiveType}}ParameterToString{{/isPrimitiveType}}{{^isPrimitiveType}}Serialize{{/isPrimitiveType}}({{paramName}})); // form parameter
                 {{/isFile}}
             }
             {{/required}}
diff --git a/samples/client/others/csharp-complex-files/src/Org.OpenAPITools/Api/MultipartApi.cs b/samples/client/others/csharp-complex-files/src/Org.OpenAPITools/Api/MultipartApi.cs
index b165faa5bd0..b8058401397 100644
--- a/samples/client/others/csharp-complex-files/src/Org.OpenAPITools/Api/MultipartApi.cs
+++ b/samples/client/others/csharp-complex-files/src/Org.OpenAPITools/Api/MultipartApi.cs
@@ -517,12 +517,12 @@ namespace Org.OpenAPITools.Api
             localVarRequestOptions.FormParameters.Add("status", Org.OpenAPITools.Client.ClientUtils.Serialize(status)); // form parameter
             if (marker != null)
             {
-                localVarRequestOptions.FormParameters.Add("marker", Org.OpenAPITools.Client.ClientUtils.ParameterToString(marker)); // form parameter
+                localVarRequestOptions.FormParameters.Add("marker", Org.OpenAPITools.Client.ClientUtils.Serialize(marker)); // form parameter
             }
             localVarRequestOptions.FileParameters.Add("file", file);
             if (statusArray != null)
             {
-                localVarRequestOptions.FormParameters.Add("statusArray", Org.OpenAPITools.Client.ClientUtils.ParameterToString(statusArray)); // form parameter
+                localVarRequestOptions.FormParameters.Add("statusArray", Org.OpenAPITools.Client.ClientUtils.Serialize(statusArray)); // form parameter
             }
 
             localVarRequestOptions.Operation = "MultipartApi.MultipartMixed";
@@ -607,15 +607,15 @@ namespace Org.OpenAPITools.Api
                 localVarRequestOptions.HeaderParameters.Add("Accept", localVarAccept);
             }
 
-            localVarRequestOptions.FormParameters.Add("status", Org.OpenAPITools.Client.ClientUtils.ParameterToString(status)); // form parameter
+            localVarRequestOptions.FormParameters.Add("status", Org.OpenAPITools.Client.ClientUtils.Serialize(status)); // form parameter
             if (marker != null)
             {
-                localVarRequestOptions.FormParameters.Add("marker", Org.OpenAPITools.Client.ClientUtils.ParameterToString(marker)); // form parameter
+                localVarRequestOptions.FormParameters.Add("marker", Org.OpenAPITools.Client.ClientUtils.Serialize(marker)); // form parameter
             }
             localVarRequestOptions.FileParameters.Add("file", file);
             if (statusArray != null)
             {
-                localVarRequestOptions.FormParameters.Add("statusArray", Org.OpenAPITools.Client.ClientUtils.ParameterToString(statusArray)); // form parameter
+                localVarRequestOptions.FormParameters.Add("statusArray", Org.OpenAPITools.Client.ClientUtils.Serialize(statusArray)); // form parameter
             }
 
             localVarRequestOptions.Operation = "MultipartApi.MultipartMixed";
diff --git a/samples/client/petstore/csharp/OpenAPIClient-ConditionalSerialization/src/Org.OpenAPITools/Api/FakeApi.cs b/samples/client/petstore/csharp/OpenAPIClient-ConditionalSerialization/src/Org.OpenAPITools/Api/FakeApi.cs
index ce37acaec65..8380cef3254 100644
--- a/samples/client/petstore/csharp/OpenAPIClient-ConditionalSerialization/src/Org.OpenAPITools/Api/FakeApi.cs
+++ b/samples/client/petstore/csharp/OpenAPIClient-ConditionalSerialization/src/Org.OpenAPITools/Api/FakeApi.cs
@@ -2858,7 +2858,7 @@ namespace Org.OpenAPITools.Api
             }
             if (enumFormStringArray != null)
             {
-                localVarRequestOptions.FormParameters.Add("enum_form_string_array", Org.OpenAPITools.Client.ClientUtils.ParameterToString(enumFormStringArray)); // form parameter
+                localVarRequestOptions.FormParameters.Add("enum_form_string_array", Org.OpenAPITools.Client.ClientUtils.Serialize(enumFormStringArray)); // form parameter
             }
             if (enumFormString != null)
             {
@@ -2969,7 +2969,7 @@ namespace Org.OpenAPITools.Api
             }
             if (enumFormStringArray != null)
             {
-                localVarRequestOptions.FormParameters.Add("enum_form_string_array", Org.OpenAPITools.Client.ClientUtils.ParameterToString(enumFormStringArray)); // form parameter
+                localVarRequestOptions.FormParameters.Add("enum_form_string_array", Org.OpenAPITools.Client.ClientUtils.Serialize(enumFormStringArray)); // form parameter
             }
             if (enumFormString != null)
             {
diff --git a/samples/client/petstore/csharp/OpenAPIClient-net47/src/Org.OpenAPITools/Api/FakeApi.cs b/samples/client/petstore/csharp/OpenAPIClient-net47/src/Org.OpenAPITools/Api/FakeApi.cs
index ce37acaec65..8380cef3254 100644
--- a/samples/client/petstore/csharp/OpenAPIClient-net47/src/Org.OpenAPITools/Api/FakeApi.cs
+++ b/samples/client/petstore/csharp/OpenAPIClient-net47/src/Org.OpenAPITools/Api/FakeApi.cs
@@ -2858,7 +2858,7 @@ namespace Org.OpenAPITools.Api
             }
             if (enumFormStringArray != null)
             {
-                localVarRequestOptions.FormParameters.Add("enum_form_string_array", Org.OpenAPITools.Client.ClientUtils.ParameterToString(enumFormStringArray)); // form parameter
+                localVarRequestOptions.FormParameters.Add("enum_form_string_array", Org.OpenAPITools.Client.ClientUtils.Serialize(enumFormStringArray)); // form parameter
             }
             if (enumFormString != null)
             {
@@ -2969,7 +2969,7 @@ namespace Org.OpenAPITools.Api
             }
             if (enumFormStringArray != null)
             {
-                localVarRequestOptions.FormParameters.Add("enum_form_string_array", Org.OpenAPITools.Client.ClientUtils.ParameterToString(enumFormStringArray)); // form parameter
+                localVarRequestOptions.FormParameters.Add("enum_form_string_array", Org.OpenAPITools.Client.ClientUtils.Serialize(enumFormStringArray)); // form parameter
             }
             if (enumFormString != null)
             {
diff --git a/samples/client/petstore/csharp/OpenAPIClient-net48/src/Org.OpenAPITools/Api/FakeApi.cs b/samples/client/petstore/csharp/OpenAPIClient-net48/src/Org.OpenAPITools/Api/FakeApi.cs
index ce37acaec65..8380cef3254 100644
--- a/samples/client/petstore/csharp/OpenAPIClient-net48/src/Org.OpenAPITools/Api/FakeApi.cs
+++ b/samples/client/petstore/csharp/OpenAPIClient-net48/src/Org.OpenAPITools/Api/FakeApi.cs
@@ -2858,7 +2858,7 @@ namespace Org.OpenAPITools.Api
             }
             if (enumFormStringArray != null)
             {
-                localVarRequestOptions.FormParameters.Add("enum_form_string_array", Org.OpenAPITools.Client.ClientUtils.ParameterToString(enumFormStringArray)); // form parameter
+                localVarRequestOptions.FormParameters.Add("enum_form_string_array", Org.OpenAPITools.Client.ClientUtils.Serialize(enumFormStringArray)); // form parameter
             }
             if (enumFormString != null)
             {
@@ -2969,7 +2969,7 @@ namespace Org.OpenAPITools.Api
             }
             if (enumFormStringArray != null)
             {
-                localVarRequestOptions.FormParameters.Add("enum_form_string_array", Org.OpenAPITools.Client.ClientUtils.ParameterToString(enumFormStringArray)); // form parameter
+                localVarRequestOptions.FormParameters.Add("enum_form_string_array", Org.OpenAPITools.Client.ClientUtils.Serialize(enumFormStringArray)); // form parameter
             }
             if (enumFormString != null)
             {
diff --git a/samples/client/petstore/csharp/OpenAPIClient-net5.0/src/Org.OpenAPITools/Api/FakeApi.cs b/samples/client/petstore/csharp/OpenAPIClient-net5.0/src/Org.OpenAPITools/Api/FakeApi.cs
index 785e887d37f..3c2b1655394 100644
--- a/samples/client/petstore/csharp/OpenAPIClient-net5.0/src/Org.OpenAPITools/Api/FakeApi.cs
+++ b/samples/client/petstore/csharp/OpenAPIClient-net5.0/src/Org.OpenAPITools/Api/FakeApi.cs
@@ -2858,7 +2858,7 @@ namespace Org.OpenAPITools.Api
             }
             if (enumFormStringArray != null)
             {
-                localVarRequestOptions.FormParameters.Add("enum_form_string_array", Org.OpenAPITools.Client.ClientUtils.ParameterToString(enumFormStringArray)); // form parameter
+                localVarRequestOptions.FormParameters.Add("enum_form_string_array", Org.OpenAPITools.Client.ClientUtils.Serialize(enumFormStringArray)); // form parameter
             }
             if (enumFormString != null)
             {
@@ -2969,7 +2969,7 @@ namespace Org.OpenAPITools.Api
             }
             if (enumFormStringArray != null)
             {
-                localVarRequestOptions.FormParameters.Add("enum_form_string_array", Org.OpenAPITools.Client.ClientUtils.ParameterToString(enumFormStringArray)); // form parameter
+                localVarRequestOptions.FormParameters.Add("enum_form_string_array", Org.OpenAPITools.Client.ClientUtils.Serialize(enumFormStringArray)); // form parameter
             }
             if (enumFormString != null)
             {
diff --git a/samples/client/petstore/csharp/OpenAPIClient/src/Org.OpenAPITools/Api/FakeApi.cs b/samples/client/petstore/csharp/OpenAPIClient/src/Org.OpenAPITools/Api/FakeApi.cs
index ce37acaec65..8380cef3254 100644
--- a/samples/client/petstore/csharp/OpenAPIClient/src/Org.OpenAPITools/Api/FakeApi.cs
+++ b/samples/client/petstore/csharp/OpenAPIClient/src/Org.OpenAPITools/Api/FakeApi.cs
@@ -2858,7 +2858,7 @@ namespace Org.OpenAPITools.Api
             }
             if (enumFormStringArray != null)
             {
-                localVarRequestOptions.FormParameters.Add("enum_form_string_array", Org.OpenAPITools.Client.ClientUtils.ParameterToString(enumFormStringArray)); // form parameter
+                localVarRequestOptions.FormParameters.Add("enum_form_string_array", Org.OpenAPITools.Client.ClientUtils.Serialize(enumFormStringArray)); // form parameter
             }
             if (enumFormString != null)
             {
@@ -2969,7 +2969,7 @@ namespace Org.OpenAPITools.Api
             }
             if (enumFormStringArray != null)
             {
-                localVarRequestOptions.FormParameters.Add("enum_form_string_array", Org.OpenAPITools.Client.ClientUtils.ParameterToString(enumFormStringArray)); // form parameter
+                localVarRequestOptions.FormParameters.Add("enum_form_string_array", Org.OpenAPITools.Client.ClientUtils.Serialize(enumFormStringArray)); // form parameter
             }
             if (enumFormString != null)
             {
diff --git a/samples/client/petstore/csharp/OpenAPIClientCore/src/Org.OpenAPITools/Api/FakeApi.cs b/samples/client/petstore/csharp/OpenAPIClientCore/src/Org.OpenAPITools/Api/FakeApi.cs
index 785e887d37f..3c2b1655394 100644
--- a/samples/client/petstore/csharp/OpenAPIClientCore/src/Org.OpenAPITools/Api/FakeApi.cs
+++ b/samples/client/petstore/csharp/OpenAPIClientCore/src/Org.OpenAPITools/Api/FakeApi.cs
@@ -2858,7 +2858,7 @@ namespace Org.OpenAPITools.Api
             }
             if (enumFormStringArray != null)
             {
-                localVarRequestOptions.FormParameters.Add("enum_form_string_array", Org.OpenAPITools.Client.ClientUtils.ParameterToString(enumFormStringArray)); // form parameter
+                localVarRequestOptions.FormParameters.Add("enum_form_string_array", Org.OpenAPITools.Client.ClientUtils.Serialize(enumFormStringArray)); // form parameter
             }
             if (enumFormString != null)
             {
@@ -2969,7 +2969,7 @@ namespace Org.OpenAPITools.Api
             }
             if (enumFormStringArray != null)
             {
-                localVarRequestOptions.FormParameters.Add("enum_form_string_array", Org.OpenAPITools.Client.ClientUtils.ParameterToString(enumFormStringArray)); // form parameter
+                localVarRequestOptions.FormParameters.Add("enum_form_string_array", Org.OpenAPITools.Client.ClientUtils.Serialize(enumFormStringArray)); // form parameter
             }
             if (enumFormString != null)
             {