Hi @zukowskig, welcome to the Community!
It’s been a while since you posted this question so you may well have already got this figured out?
If not, just thought I’d mention that the POST (Webhooks by Zapier) action has a File field and if you select a file object for it (from a previous trigger or action in the Zap), it will automatically convert it to use the multipart/form-data Content Type:
I’ve not tested it with Gong’s API but I’ve used it before to send files to apps via a webhook in the past and it’s worked.
If you do manage to get it working using that File field please let us know, would love to know for whether that solves it!