diff --git a/modules/openapi-generator/src/main/resources/swift6/APIs.mustache b/modules/openapi-generator/src/main/resources/swift6/APIs.mustache
index 55ed0a08b51..c0080c12ba2 100644
--- a/modules/openapi-generator/src/main/resources/swift6/APIs.mustache
+++ b/modules/openapi-generator/src/main/resources/swift6/APIs.mustache
@@ -104,6 +104,7 @@ import Alamofire{{/useAlamofire}}
         self.openAPIClient = openAPIClient
 
         addHeaders(openAPIClient.customHeaders)
+        addCredential()
     }
 
     {{#nonPublicApi}}internal{{/nonPublicApi}}{{^nonPublicApi}}open{{/nonPublicApi}} func addHeaders(_ aHeaders: [String: String]) {
@@ -161,9 +162,8 @@ import Alamofire{{/useAlamofire}}
         return self
     }
 
-    {{#nonPublicApi}}internal{{/nonPublicApi}}{{^nonPublicApi}}open{{/nonPublicApi}} func addCredential() -> Self {
+    {{#nonPublicApi}}internal{{/nonPublicApi}}{{^nonPublicApi}}open{{/nonPublicApi}} func addCredential() {
         credential = openAPIClient.credential
-        return self
     }
 }
 
diff --git a/samples/client/petstore/swift6/alamofireLibrary/Sources/PetstoreClient/Infrastructure/APIs.swift b/samples/client/petstore/swift6/alamofireLibrary/Sources/PetstoreClient/Infrastructure/APIs.swift
index cc25ab3ee26..a5313388c63 100644
--- a/samples/client/petstore/swift6/alamofireLibrary/Sources/PetstoreClient/Infrastructure/APIs.swift
+++ b/samples/client/petstore/swift6/alamofireLibrary/Sources/PetstoreClient/Infrastructure/APIs.swift
@@ -83,6 +83,7 @@ open class RequestBuilder<T>: @unchecked Sendable {
         self.openAPIClient = openAPIClient
 
         addHeaders(openAPIClient.customHeaders)
+        addCredential()
     }
 
     open func addHeaders(_ aHeaders: [String: String]) {
@@ -103,9 +104,8 @@ open class RequestBuilder<T>: @unchecked Sendable {
         return self
     }
 
-    open func addCredential() -> Self {
+    open func addCredential() {
         credential = openAPIClient.credential
-        return self
     }
 }
 
diff --git a/samples/client/petstore/swift6/apiNonStaticMethod/Sources/PetstoreClient/Infrastructure/APIs.swift b/samples/client/petstore/swift6/apiNonStaticMethod/Sources/PetstoreClient/Infrastructure/APIs.swift
index 52ff5ed4ba1..2beb10b49b3 100644
--- a/samples/client/petstore/swift6/apiNonStaticMethod/Sources/PetstoreClient/Infrastructure/APIs.swift
+++ b/samples/client/petstore/swift6/apiNonStaticMethod/Sources/PetstoreClient/Infrastructure/APIs.swift
@@ -83,6 +83,7 @@ open class RequestBuilder<T>: @unchecked Sendable {
         self.openAPIClient = openAPIClient
 
         addHeaders(openAPIClient.customHeaders)
+        addCredential()
     }
 
     open func addHeaders(_ aHeaders: [String: String]) {
@@ -138,9 +139,8 @@ open class RequestBuilder<T>: @unchecked Sendable {
         return self
     }
 
-    open func addCredential() -> Self {
+    open func addCredential() {
         credential = openAPIClient.credential
-        return self
     }
 }
 
diff --git a/samples/client/petstore/swift6/asyncAwaitLibrary/Sources/PetstoreClient/Infrastructure/APIs.swift b/samples/client/petstore/swift6/asyncAwaitLibrary/Sources/PetstoreClient/Infrastructure/APIs.swift
index d4ad3ddd865..780dd6dd1a5 100644
--- a/samples/client/petstore/swift6/asyncAwaitLibrary/Sources/PetstoreClient/Infrastructure/APIs.swift
+++ b/samples/client/petstore/swift6/asyncAwaitLibrary/Sources/PetstoreClient/Infrastructure/APIs.swift
@@ -69,6 +69,7 @@ open class RequestBuilder<T>: @unchecked Sendable {
         self.openAPIClient = openAPIClient
 
         addHeaders(openAPIClient.customHeaders)
+        addCredential()
     }
 
     open func addHeaders(_ aHeaders: [String: String]) {
@@ -124,9 +125,8 @@ open class RequestBuilder<T>: @unchecked Sendable {
         return self
     }
 
-    open func addCredential() -> Self {
+    open func addCredential() {
         credential = openAPIClient.credential
-        return self
     }
 }
 
diff --git a/samples/client/petstore/swift6/combineDeferredLibrary/PetstoreClient/Classes/OpenAPIs/Infrastructure/APIs.swift b/samples/client/petstore/swift6/combineDeferredLibrary/PetstoreClient/Classes/OpenAPIs/Infrastructure/APIs.swift
index 53681863380..c3acec934bb 100644
--- a/samples/client/petstore/swift6/combineDeferredLibrary/PetstoreClient/Classes/OpenAPIs/Infrastructure/APIs.swift
+++ b/samples/client/petstore/swift6/combineDeferredLibrary/PetstoreClient/Classes/OpenAPIs/Infrastructure/APIs.swift
@@ -69,6 +69,7 @@ open class RequestBuilder<T>: @unchecked Sendable {
         self.openAPIClient = openAPIClient
 
         addHeaders(openAPIClient.customHeaders)
+        addCredential()
     }
 
     open func addHeaders(_ aHeaders: [String: String]) {
@@ -89,9 +90,8 @@ open class RequestBuilder<T>: @unchecked Sendable {
         return self
     }
 
-    open func addCredential() -> Self {
+    open func addCredential() {
         credential = openAPIClient.credential
-        return self
     }
 }
 
diff --git a/samples/client/petstore/swift6/combineLibrary/Sources/CombineLibrary/Infrastructure/APIs.swift b/samples/client/petstore/swift6/combineLibrary/Sources/CombineLibrary/Infrastructure/APIs.swift
index 53681863380..c3acec934bb 100644
--- a/samples/client/petstore/swift6/combineLibrary/Sources/CombineLibrary/Infrastructure/APIs.swift
+++ b/samples/client/petstore/swift6/combineLibrary/Sources/CombineLibrary/Infrastructure/APIs.swift
@@ -69,6 +69,7 @@ open class RequestBuilder<T>: @unchecked Sendable {
         self.openAPIClient = openAPIClient
 
         addHeaders(openAPIClient.customHeaders)
+        addCredential()
     }
 
     open func addHeaders(_ aHeaders: [String: String]) {
@@ -89,9 +90,8 @@ open class RequestBuilder<T>: @unchecked Sendable {
         return self
     }
 
-    open func addCredential() -> Self {
+    open func addCredential() {
         credential = openAPIClient.credential
-        return self
     }
 }
 
diff --git a/samples/client/petstore/swift6/default/Sources/PetstoreClient/Infrastructure/APIs.swift b/samples/client/petstore/swift6/default/Sources/PetstoreClient/Infrastructure/APIs.swift
index d4ad3ddd865..780dd6dd1a5 100644
--- a/samples/client/petstore/swift6/default/Sources/PetstoreClient/Infrastructure/APIs.swift
+++ b/samples/client/petstore/swift6/default/Sources/PetstoreClient/Infrastructure/APIs.swift
@@ -69,6 +69,7 @@ open class RequestBuilder<T>: @unchecked Sendable {
         self.openAPIClient = openAPIClient
 
         addHeaders(openAPIClient.customHeaders)
+        addCredential()
     }
 
     open func addHeaders(_ aHeaders: [String: String]) {
@@ -124,9 +125,8 @@ open class RequestBuilder<T>: @unchecked Sendable {
         return self
     }
 
-    open func addCredential() -> Self {
+    open func addCredential() {
         credential = openAPIClient.credential
-        return self
     }
 }
 
diff --git a/samples/client/petstore/swift6/objcCompatible/Sources/PetstoreClient/Infrastructure/APIs.swift b/samples/client/petstore/swift6/objcCompatible/Sources/PetstoreClient/Infrastructure/APIs.swift
index 53681863380..c3acec934bb 100644
--- a/samples/client/petstore/swift6/objcCompatible/Sources/PetstoreClient/Infrastructure/APIs.swift
+++ b/samples/client/petstore/swift6/objcCompatible/Sources/PetstoreClient/Infrastructure/APIs.swift
@@ -69,6 +69,7 @@ open class RequestBuilder<T>: @unchecked Sendable {
         self.openAPIClient = openAPIClient
 
         addHeaders(openAPIClient.customHeaders)
+        addCredential()
     }
 
     open func addHeaders(_ aHeaders: [String: String]) {
@@ -89,9 +90,8 @@ open class RequestBuilder<T>: @unchecked Sendable {
         return self
     }
 
-    open func addCredential() -> Self {
+    open func addCredential() {
         credential = openAPIClient.credential
-        return self
     }
 }
 
diff --git a/samples/client/petstore/swift6/oneOf/PetstoreClient/Classes/OpenAPIs/Infrastructure/APIs.swift b/samples/client/petstore/swift6/oneOf/PetstoreClient/Classes/OpenAPIs/Infrastructure/APIs.swift
index f16a75b3232..4cdb41e1204 100644
--- a/samples/client/petstore/swift6/oneOf/PetstoreClient/Classes/OpenAPIs/Infrastructure/APIs.swift
+++ b/samples/client/petstore/swift6/oneOf/PetstoreClient/Classes/OpenAPIs/Infrastructure/APIs.swift
@@ -69,6 +69,7 @@ open class RequestBuilder<T>: @unchecked Sendable {
         self.openAPIClient = openAPIClient
 
         addHeaders(openAPIClient.customHeaders)
+        addCredential()
     }
 
     open func addHeaders(_ aHeaders: [String: String]) {
@@ -89,9 +90,8 @@ open class RequestBuilder<T>: @unchecked Sendable {
         return self
     }
 
-    open func addCredential() -> Self {
+    open func addCredential() {
         credential = openAPIClient.credential
-        return self
     }
 }
 
diff --git a/samples/client/petstore/swift6/promisekitLibrary/PetstoreClient/Classes/OpenAPIs/Infrastructure/APIs.swift b/samples/client/petstore/swift6/promisekitLibrary/PetstoreClient/Classes/OpenAPIs/Infrastructure/APIs.swift
index 53681863380..c3acec934bb 100644
--- a/samples/client/petstore/swift6/promisekitLibrary/PetstoreClient/Classes/OpenAPIs/Infrastructure/APIs.swift
+++ b/samples/client/petstore/swift6/promisekitLibrary/PetstoreClient/Classes/OpenAPIs/Infrastructure/APIs.swift
@@ -69,6 +69,7 @@ open class RequestBuilder<T>: @unchecked Sendable {
         self.openAPIClient = openAPIClient
 
         addHeaders(openAPIClient.customHeaders)
+        addCredential()
     }
 
     open func addHeaders(_ aHeaders: [String: String]) {
@@ -89,9 +90,8 @@ open class RequestBuilder<T>: @unchecked Sendable {
         return self
     }
 
-    open func addCredential() -> Self {
+    open func addCredential() {
         credential = openAPIClient.credential
-        return self
     }
 }
 
diff --git a/samples/client/petstore/swift6/resultLibrary/PetstoreClient/Classes/OpenAPIs/Infrastructure/APIs.swift b/samples/client/petstore/swift6/resultLibrary/PetstoreClient/Classes/OpenAPIs/Infrastructure/APIs.swift
index 48912d8a359..7d8c0e7aaea 100644
--- a/samples/client/petstore/swift6/resultLibrary/PetstoreClient/Classes/OpenAPIs/Infrastructure/APIs.swift
+++ b/samples/client/petstore/swift6/resultLibrary/PetstoreClient/Classes/OpenAPIs/Infrastructure/APIs.swift
@@ -69,6 +69,7 @@ internal class RequestBuilder<T>: @unchecked Sendable {
         self.openAPIClient = openAPIClient
 
         addHeaders(openAPIClient.customHeaders)
+        addCredential()
     }
 
     internal func addHeaders(_ aHeaders: [String: String]) {
@@ -89,9 +90,8 @@ internal class RequestBuilder<T>: @unchecked Sendable {
         return self
     }
 
-    internal func addCredential() -> Self {
+    internal func addCredential() {
         credential = openAPIClient.credential
-        return self
     }
 }
 
diff --git a/samples/client/petstore/swift6/rxswiftLibrary/PetstoreClient/Classes/OpenAPIs/Infrastructure/APIs.swift b/samples/client/petstore/swift6/rxswiftLibrary/PetstoreClient/Classes/OpenAPIs/Infrastructure/APIs.swift
index 53681863380..c3acec934bb 100644
--- a/samples/client/petstore/swift6/rxswiftLibrary/PetstoreClient/Classes/OpenAPIs/Infrastructure/APIs.swift
+++ b/samples/client/petstore/swift6/rxswiftLibrary/PetstoreClient/Classes/OpenAPIs/Infrastructure/APIs.swift
@@ -69,6 +69,7 @@ open class RequestBuilder<T>: @unchecked Sendable {
         self.openAPIClient = openAPIClient
 
         addHeaders(openAPIClient.customHeaders)
+        addCredential()
     }
 
     open func addHeaders(_ aHeaders: [String: String]) {
@@ -89,9 +90,8 @@ open class RequestBuilder<T>: @unchecked Sendable {
         return self
     }
 
-    open func addCredential() -> Self {
+    open func addCredential() {
         credential = openAPIClient.credential
-        return self
     }
 }
 
diff --git a/samples/client/petstore/swift6/urlsessionLibrary/Sources/PetstoreClient/Infrastructure/APIs.swift b/samples/client/petstore/swift6/urlsessionLibrary/Sources/PetstoreClient/Infrastructure/APIs.swift
index 65224277042..86016f1efe9 100644
--- a/samples/client/petstore/swift6/urlsessionLibrary/Sources/PetstoreClient/Infrastructure/APIs.swift
+++ b/samples/client/petstore/swift6/urlsessionLibrary/Sources/PetstoreClient/Infrastructure/APIs.swift
@@ -71,6 +71,7 @@ open class RequestBuilder<T>: @unchecked Sendable {
         self.openAPIClient = openAPIClient
 
         addHeaders(openAPIClient.customHeaders)
+        addCredential()
     }
 
     open func addHeaders(_ aHeaders: [String: String]) {
@@ -91,9 +92,8 @@ open class RequestBuilder<T>: @unchecked Sendable {
         return self
     }
 
-    open func addCredential() -> Self {
+    open func addCredential() {
         credential = openAPIClient.credential
-        return self
     }
 }
 
diff --git a/samples/client/petstore/swift6/validation/PetstoreClient/Classes/OpenAPIs/Infrastructure/APIs.swift b/samples/client/petstore/swift6/validation/PetstoreClient/Classes/OpenAPIs/Infrastructure/APIs.swift
index 362d9ce5333..78354f00789 100644
--- a/samples/client/petstore/swift6/validation/PetstoreClient/Classes/OpenAPIs/Infrastructure/APIs.swift
+++ b/samples/client/petstore/swift6/validation/PetstoreClient/Classes/OpenAPIs/Infrastructure/APIs.swift
@@ -69,6 +69,7 @@ open class RequestBuilder<T>: @unchecked Sendable {
         self.openAPIClient = openAPIClient
 
         addHeaders(openAPIClient.customHeaders)
+        addCredential()
     }
 
     open func addHeaders(_ aHeaders: [String: String]) {
@@ -124,9 +125,8 @@ open class RequestBuilder<T>: @unchecked Sendable {
         return self
     }
 
-    open func addCredential() -> Self {
+    open func addCredential() {
         credential = openAPIClient.credential
-        return self
     }
 }