Mexico Electronic Invoice Functionality - error on SignData

Hi everyone - this is almost a mayday call for help.

My customer is still on NAV2009R2. They have the need for the Mexico SAT stamping functionality.

I have brought in all the needed code (Code Units, Tables, Reports, and the MX.SignatureProvider Dll's), all the code compiles.

I imported the certificate provided and added the Thumbprint to the Thumbprint field in NAV.

Unfortunately, the process of requesting the stamp fails with the following message:

This message is for C/AL programmers: The call to member SignData failed : The FileName of the file to be signed is invalid : Parameter Name : OriginalValueFileName

I have no idea how to resolve this issue. Is there anyone who has been successful in implementing this who is willing to help me?