TrustPilot Create Invitation API always returns 415 response code

I'm trying to send a TrustPilot invitation using the Create Invitations API but no matter what I try, I get a response code of 415 and with no data returned, so it's virtually impossible for me to debug.

• The URL I'm using is correct: https://invitations-api.trustpilot.com/v1/private/business-units/{businessUnitId}/email-invitations (where {businessUnitId} is my business ID)
• I am sending a valid (and current) oAuth token in my header.
• I am sending a POST request.

I have tested my details with other "Business user OAuth Token" APIs and everything works, so my details are definitely correct. It's just this create invitation API that's not working.

I've tried everything. I've submitted minimal details, a full request, somewhere in between, the example request in the API, and so on. Always a response code of 415.

I've set my "Invitation Settings" in the TrustPilot Business portal, and have even tried submitting those details with the request (ie. sender e-mail "noreply.invitations@trustpilotmail.com" and a valid reply-to e-mail that's been configured).

I've tried contacting the "Integration Engineers" at TrustPilot who after a few back and forth e-mails, also have no idea, which is VERY unsettling. So time for Stack Overflow.

I need to get this figured out, so any help would be great! Perhaps someone can provide a sample request that works in their application that I can try to duplicate in mine?

Http status code 415 (Unsupported Media Type) is returned when Content-Type: application/json is not passed. You need to make sure that this header is added and that the content you are passing in the post body is valid json.

If you are already doing this then I would need an example of a request you are sending to help you further.