My name is Rae and I work for Shopify.
I understand how important this integration is for your store, and I'd like to help get this resolved.
Once you've confirmed those details, can you tell me a bit more about the error you mentioned? For instance, where are you seeing the 'can't publish' message? Is this appearing on Facebook, or in your Shopify admin?
Can you also please send me a screenshot showing the exact error message you're receiving? This will help me look into things further. However, before sharing this image in a reply to me here, I recommend blocking out any sensitive or store-specific details.
I look forward to hearing back from you with this information!