diff --git a/templates/go/api.mustache b/templates/go/api.mustache
index c5b644b7dc..0804ec8718 100644
--- a/templates/go/api.mustache
+++ b/templates/go/api.mustache
@@ -459,19 +459,7 @@ func (c *APIClient) {{nickname}}({{#hasParams}}r {{#structPrefix}}{{&classname}}
   }
 
 	if res.StatusCode >= 300 {
-		newErr := &APIError{
-      Message: string(resBody),
-			Status: res.StatusCode,
-		}
-
-    var v ErrorBase
-    err = c.decode(&v, resBody)
-    if err != nil {
-      newErr.Message = err.Error()
-      return {{#returnType}}returnValue, {{/returnType}}newErr
-    }
-
-		return {{#returnType}}returnValue, {{/returnType}}newErr
+			return {{#returnType}}returnValue, {{/returnType}}c.decodeError(res, resBody)
 	}
 
 	{{#returnType}}
diff --git a/templates/go/client.mustache b/templates/go/client.mustache
index 577fc7491d..6a202a78af 100644
--- a/templates/go/client.mustache
+++ b/templates/go/client.mustache
@@ -234,7 +234,7 @@ func (c *APIClient) decode(v any, b []byte) error {
         return fmt.Errorf("failed to unmarshal one of in response body: %w", err)
       }
     } else {
-      return errors.New("Unknown type with GetActualInstance but no unmarshalObj.UnmarshalJSON defined")
+      return errors.New("unknown type with GetActualInstance but no unmarshalObj.UnmarshalJSON defined")
     }
   } else if err := json.Unmarshal(b, v); err != nil { // simple model
     return fmt.Errorf("failed to unmarshal response body: %w", err)
@@ -243,6 +243,33 @@ func (c *APIClient) decode(v any, b []byte) error {
   return nil
 }
 
+func (c *APIClient) decodeError(res *http.Response, body []byte) error {
+  apiErr := &APIError{
+    Message: string(body), // default to the full body if we cannot guess the type of the error.
+    Status:  res.StatusCode,
+  }
+
+  if strings.Contains(res.Header.Get("Content-Type"), "application/json") {
+    var errBase ErrorBase
+
+    err := c.decode(&errBase, body)
+		if err != nil {
+			apiErr.Message = err.Error()
+
+			return apiErr
+		}
+    if errBase.Message != nil {
+      apiErr.Message = *errBase.Message
+    }
+
+    apiErr.AdditionalProperties = errBase.AdditionalProperties
+  } else if strings.Contains(res.Header.Get("Content-Type"), "text/html") {
+    apiErr.Message = http.StatusText(res.StatusCode)
+  }
+
+  return apiErr
+}
+
 // Prevent trying to import "fmt"
 func reportError(format string, a ...any) error {
 	return fmt.Errorf(format, a...)
@@ -299,7 +326,7 @@ func setBody(body any, c compression.Compression) (*bytes.Buffer, error) {
 	}
 
 	if bodyBuf.Len() == 0 {
-		return nil, errors.New("Invalid body type, or empty body")
+		return nil, errors.New("invalid body type, or empty body")
 	}
 	return bodyBuf, nil
 }
@@ -307,8 +334,50 @@ func setBody(body any, c compression.Compression) (*bytes.Buffer, error) {
 type APIError struct {
 	Message string
   Status int
+  AdditionalProperties map[string]any
 }
 
 func (e APIError) Error() string {
 	return fmt.Sprintf("API error [%d] %s", e.Status, e.Message)
 }
+
+func (o APIError) MarshalJSON() ([]byte, error) {
+	toSerialize := map[string]any{
+    "message": o.Message,
+  }
+
+	for key, value := range o.AdditionalProperties {
+		toSerialize[key] = value
+	}
+
+	serialized, err := json.Marshal(toSerialize)
+	if err != nil {
+		return nil, fmt.Errorf("failed to marshal APIError: %w", err)
+	}
+
+	return serialized, nil
+}
+
+func (o *APIError) UnmarshalJSON(bytes []byte) error {
+  type _APIError APIError
+	apiErr := _APIError{}
+
+	err := json.Unmarshal(bytes, &apiErr)
+	if err != nil {
+		return fmt.Errorf("failed to unmarshal APIError: %w", err)
+	}
+
+	*o = APIError(apiErr)
+
+	additionalProperties := make(map[string]any)
+
+	err = json.Unmarshal(bytes, &additionalProperties)
+	if err != nil {
+		return fmt.Errorf("failed to unmarshal additionalProperties in APIError: %w", err)
+	}
+
+	delete(additionalProperties, "message")
+	o.AdditionalProperties = additionalProperties
+
+	return nil
+}
diff --git a/tests/CTS/client/search/indexExists.json b/tests/CTS/client/search/indexExists.json
index ab609f9d6f..fab0be4263 100644
--- a/tests/CTS/client/search/indexExists.json
+++ b/tests/CTS/client/search/indexExists.json
@@ -82,7 +82,7 @@
         "expected": {
           "error": {
             "csharp": "{\\\"message\\\":\\\"Invalid API key\\\"}",
-            "go": "API error [403] {\\\"message\\\":\\\"Invalid API key\\\"}",
+            "go": "API error [403] Invalid API key",
             "java": "Status Code: 403 - {\\\"message\\\":\\\"Invalid API key\\\"}",
             "javascript": "Invalid API key",
             "kotlin": "Client request(GET http://%localhost%:6681/1/indexes/indexExistsERROR/settings) invalid: 403 Forbidden. Text: \\\"{\\\"message\\\":\\\"Invalid API key\\\"}\\\"",
diff --git a/tests/CTS/client/search/saveObjects.json b/tests/CTS/client/search/saveObjects.json
index b461f75cd5..2c594f6424 100644
--- a/tests/CTS/client/search/saveObjects.json
+++ b/tests/CTS/client/search/saveObjects.json
@@ -81,7 +81,7 @@
         "expected": {
           "error": {
             "csharp": "{\\\"message\\\":\\\"Invalid Application-ID or API key\\\",\\\"status\\\":403}",
-            "go": "API error [403] {\\\"message\\\":\\\"Invalid Application-ID or API key\\\",\\\"status\\\":403}",
+            "go": "API error [403] Invalid Application-ID or API key",
             "java": "Status Code: 403 - {\\\"message\\\":\\\"Invalid Application-ID or API key\\\",\\\"status\\\":403}",
             "javascript": "Invalid Application-ID or API key",
             "kotlin": "Client request(POST http://%localhost%:6680/1/indexes/cts_e2e_saveObjects_kotlin/batch) invalid: 403 Forbidden. Text: \\\"{\\\"message\\\":\\\"Invalid Application-ID or API key\\\",\\\"status\\\":403}\\\"",