Hi Allen,
Thanks for following up.
When I say self contained, I meant having a single command for the CURL command - so all the data is is there - not having to refer to an external file to refer-to/attach.
The reason I sent my query by this forum was to get the CURL syntax correct in Postman (which is why I mainly use Postman. Testing). The final command syntax is written in Filemaker but needed to understand the native CURL syntax before I could use it.
I have made progress on this overnight (amazing what you can achieve when you don’t sleep. 
) and am close.
Thank you for your (and others’) help on this. Further testing and Googling the stuffing out of this I might have cracked it by the end of today.
Cheers Allen.