Had you previously provided a different SSN number in the Shopify Payments settings? As once the information is provided, it is not possible to edit the details of your Shopify Payments account. If there is a need to change these details, requests should be escalated to our support team here at this link and must come from the account owner on file.
You can also check out this page here which walks through the documents and requirements for Shopify Payments.
Aside from this, how is everything else going? Are you just starting out? If so, we have a great checklist that can help with getting set up and ready to sell - click here!
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