API problems

Has anyone been successful updating a user's profile (specifically their avatar) using the API? I can't seem to get it to work using either a Formidable Forms API action or via a FlowMattic API action

For example, I can do a get to this url (https://fc.topleveldomain.org/wp-json/fluent-community/v2/profile/1234567) and it returns all the user information. This validates that I have all the authentication, etc. correct.

However, when I do a post to that same url and pass in the following json to update the avatar
{
"avatar": "https://fc.topleveldomain.org/wp-content/uploads/formidable/50/3879-6-150x150.jpg"
}

I get the following error:

No query results for model [FluentCommunity\\App\\Models\\XProfile].

This seems to imply that the username I'm passing in (1234567) can't be found when doing the post but the same url works for getting the profile info.

Anyone have any idea on how to resolve this? Shahjahan Jewel 

Thanks in advance!