User Avatar API Endpoint 404 on POST, 200 on GET

We don't directly use PUT requests in REST, instead we use a POST request with a Rest-Method header of PUT.  There is an example and explanation here:  https://community.telligent.com/community/12/a/developer-training/DT14/making-requests#put

Try switching to a POST request in Postman and adding the Rest-Method header PUT.

This is unrelated to my first question, however if there a way to set a users avatar to something from the "Select Avatar" options? I am passing in the URL to those avatars, however it wont work because the site is not configured to allow for remote avatars.

It is looking for an exact match on the Url of a selectable avatar.  You will need the original url rather than a resized image url. Those Urls don't appear to be visible anywhere in administration, but if you go to edit your profile and change your avatar, you can see them by inspect the images and looking for the data-url property.  Or just adjust the format of the resized image urls to match the following one.

It should look like this:  /cfs-file/__key/communityserver-discussions-components-files/3048/avatar.png

It is looking for an exact match on the Url of a selectable avatar.  You will need the original url rather than a resized image url. Those Urls don't appear to be visible anywhere in administration, but if you go to edit your profile and change your avatar, you can see them by inspect the images and looking for the data-url property.  Or just adjust the format of the resized image urls to match the following one.

It should look like this:  /cfs-file/__key/communityserver-discussions-components-files/3048/avatar.png

Thank you! I am still getting the remote avatars are disabled, while passing this in as a AvatarUrl /cfs-file/__key/communityserver-components-selectableavatars/fc914bac-2325-492c-b53f-6c375c85aa7d/avatar.png

You are correct, there is a check in the code that cannot be bypassed when using the REST API.   There is no workaround (other than enabling remote avatars while performing the update) and it will require a bug fix to address the issue in the API.

A bug has been filed to have this looked at.

Thank you! Should this work using the In-Process API?

The issue is in code that is shared across all the User Avatar APIs.  It only works on the site, because that popup uses some old internal code to set the avatar.

Thank you for all this information! My last question on this; is it possible to enable remote URLs to get this to work, but modify the Avatar page to hide the URL input?

In Widget Studio, in the Viewing dropdown, scroll down to Extensions and you should see Change User Avatar Modal.  That should be the widget that defines that modal.   You should be able to alter that widget to alter what inputs are available.