Do not have customers complete all pertinent payment info, THEN ask for a sign in, THEN require reentry of payment info. That happened to me three times. Just make sure the sign-in is required first, and make sure customers know it's the Intuit sign-in and not the vendor's sign-in we are completing.

Also putting a label of "Subject" in the top box above would be useful. With the question above it, a reader's default is to answer the question in the top box.