Your payouts from Shopify Payments are on hold because additional details about your business are required. Your customers can still checkout while your payouts are on hold.
But it doesn't tell me what I need to do to get it unlocked. I've clicked contact shopify but it just sends me on a merry dance around the support section without an email address or real person to talk to.
Eunice here from the Shopify Community. Thanks for posting!
I'm sorry you're having difficulty reaching out to the support team. You can chat with a Support advisor 24/7 here.
Without looking into your store I'm unable to confirm what this particular error message means for you, as there could be a number of reasons why payments have been put on hold. But usually, in cases like these, there should be an option for you to submit documents from your Shopify admin. The option to do this will be in a colored box located under where the error message populated. Do you see that?
Not to worry if you don't. I've already sent you an email to your Community email address, just respond to me there and I'll look into this for you.