Using DllExport utility and class I'm having some troubles with the declaration.

Here is my C# function

 [DllExport("ValidatePass", System.Runtime.InteropServices.CallingConvention.StdCall)]
        /// <summary>
        /// ValidatePass function
        
        /// <param name="tcBarcode">Barcode - The DLL will package up the tcBarcode and tcUsageDate into simple JSON</param>
        /// <param name="tcUsageDate">Datetime of the scan converted into the necessary string format</param>
        
        /// <param name="tnRetries">If no response in the timeout period, the number of times to attempt contact . 
        ///                         If it was a DNS lookup failure or other glaring connection issue, then retries can be bypassed..</param>
        /// <param name="tnReturnValue">Passed by reference, it is the “ReturnValue” string in the JSON response</param>
        /// <param name="tcReturnValueText">Passed by reference, it is the “ReturnValueText” string in the JSON response</param>
        /// <param name="tcMessage">“Message” string in the JSON response, if present</param>
        /// <param name="tcProductCode">“ExternalProductCode” string in the JSON response, if present</param>
        /// <returns>int Status</returns> 
        /// </summary>        
        public static int ValidatePass(String tcBarcode,
                      String tcUsageDate, Int32 tnRetries,
                      ref Int32 tnReturnValue, ref String tcReturnValueText, ref String tcMessage, ref String tcProductCode)

and this is my VFP declaration

declare integer ValidatePass in "myDll.dll" ;
		string, string, integer, @integer, @string, @string, @string

and attempt to call it

result = ValidatePass("01120800369238", "2016-10-28T15:09:06.7021957-06:00", 3, ;
		@ReturnValue, @ReturnValueText, @cMessage, @ProductCode)

However, I am getting 'Too many arguments' error on that line (2 other functions that only set static properties seem to work fine).

Can I have function in VFP with many parameters passed by reference? Could the problem be in the integer return value by reference?

Thanks in advance.