Hank here from Shopify.
That message normally appears when there is an outstanding charge due to an invoice already having been issued. But normally when the invoice is related to non Shopify charges, like a third-party app, or tax, transaction fees or shipping charges.
Do you see something similar within your admin when you go to Settings > Billing? You should be able to view the details of the invoice.
I will also share how to close your store within your admin by yourself if you are able to clear the invoice.
Let me know if this is is similar, or if you have any further questions, I may be able to look into this for you.
All the best,