What's keeping me from becoming a Rover sitter?

I was previously a sitter at DogVacay until they chose to merge with you guys (Rover). But when this happened, I stopped receiving requests from clients and I think it's because the website required me to do a background check. However, I can't complete this process when I don't have an SSN (Social Security Number). Please let me know what I can do. Thank you and have a good day :)