How do I name an attached pdf document with a name differing from its file path name, using a curl script?

A curl example formulated at https://developers.ringcentral.com/api-reference/Fax/createFaxMessage yields the following data string:

--data '{"attachment":"data:application/pdf;name=A%20different%20name.pdf;base64,<<base64>>","to":["1234567890"] }'.

I created a curl data post, which delivered a fully rendered pdf, but without a new name using the following string:

"-F "attachment=@$PDF_Container_Field;name=A%20different%20name.pdf;type=application/pdf" -F "to=" & $toRecipientTenDigit & "" "

As an aside, regarding my not using base64 encoding, my script is executed via FilemakerPro via "insert from url" with curl options. I guess that base64 encoding occurs when a curl option -F is streamed via Filemaker's "insert from url" command, as the script delivers a fully rendered pdf.

Question:

What might be correct curl syntax possibilities to simulate the syntax found in the curl command generated at developers.ringcentral.com/api-reference/Fax/createFaxMessage?