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Your API documentation only shows this as a form submission but we are trying to do this without user interaction.

I think what I may be missing is the content type for the CreateUserProfileImageRequest attachment.

using C# this is what I tried. Error was "the format of value 'image' is invalid.

byte[] b = System.IO.File.ReadAllBytes(@"C:\Users\cacarey\Documents\iface.jpg");


            CreateUserProfileImageRequest cp = new CreateUserProfileImageRequest();
            RingCentral.Attachment att = new Attachment();
            att.filename = "iface.jpg";
            att.content = b;
            att.contentType = "image";
            cp.image = att;


            
            var rr = await restClient.Restapi().Account(accountID).Extension(extID).ProfileImage().Post(cp);