Rae from Shopify here. Thanks for reaching out with this question regarding your Facebook account, and welcome to the Shopify Community.
To confirm, is this error message appearing directly in the 'Facebook' section of your Shopify admin, or is this showing up on Facebook's end? So that I can help look into this further, can you please send me a screenshot of this error message?
In the meantime though, there are a few troubleshooting steps that I recommend taking:
Once you've completed these steps, please let me know if the error message is still appearing. If it is, just reply back to me here with a screenshot of this error and I can certainly help provide more assistance.
I look forward to hearing back from you about this!