Hi @AlleyMcB, glad to help with your question. Yes AlleyMcB, You could try adding the Facebook channel to your Shopify store again. Sometimes it can reset the relationship between Shopify and Facebook.
For Facebook checkout follow these steps:
Log into Shopify and select +(plus icon) next to the sales channels
Select Learn More next to the Facebook channel
Click Add channel
Next, select Facebook and click Get Started
Click Connect Account
Hopefully, that solves your problem. If not, please let me know if you're seeing any other issues.