Were you on Managed Payments last time you sold?
Make sure you are using a valid US street mailing address (not a PO Box) and a US phone number.
The address must match the info on your bank account exactly, as your name must.
I think that there is a limit to the number of times you can try to validate a phone number, so if you have tried several times in one day, you may have to wait until the next day to try again.
If your phone number is a number that can receive texts, try validating your phone number using the eBay app.
I seem to recall an issue previously where users trying to validate a phone number had better results when changing the country code to Canada.
