post
https://api.sintalk.com.br/v3/files//confirm
Step 3 of the three-step direct upload: once the PUT to the presigned URL succeeds, confirm the file so it can be used. status flips from pending to uploaded.
Confirming a file that is already uploaded returns the same result, so a retry is safe. Confirming before the bytes reach storage returns 409 and leaves the file pending, so it can be confirmed again after the upload completes.