I would be happy to help.
I created for a client the Filemaker --> Google Calendar connection using the API, so I should be able to help you effectively.
In my case, I used the BaseElements plugin functions, rather than the FM cUrl feature, but I'm actually using FM cUrl with several APIs, so I know quite well what you are talking about.
My experience tells me that the error can be solved very quickly, but this action could solve hours of headache!
Ready to start,,,
Alex