As you'd like the written reply addressed.
Use the same address as your Stripe receipt so we can match your upload to your payment. Wrong email address slows everything down.
Starts "rcpt_" or looks like 1234-5678. Check your Stripe email if handy. Skip if you do not have it, we can still find you by email.
One letter, one sender. Every page, front and back. Add each page as a separate file, or upload one multi-page PDF. Phone photo is fine, no need to scan.
One line if there is something else that would help. A deadline you are worried about, who the letter is from if it is not obvious, or what is making you unsure.