Client Letter / Contract Letter

I have been asked to provide client letter signed by end client and on client’s letterhead. But my onsite manager told me that it is impossible to get this letter.
So I am going with letter having details of client and signed by my onsite manager. Is it going to resolve the issue?
Also I have abeen asked to provide contract letter. Can I provide SOW for this query?

ask your onsite manager how he has been addressing such issues for the other visa holder stamping? They must be having an alternate work around.

Ideally, if your client is not giving, ask them to give in writing that “our company polices doesnt allow such letter to be issued” or something like that.

Keep that email or letter copy along with few latest email communication with your office/manager, your employee page on clients intranet page, badge copy and any other close proofs that you are working at the client place, along with the MSA/SOW with your client .