I’m sorry! I’ve found directly launching a Facebook Shop difficult and cumbersome, and hard to connect payments etc. Basically, I couldn’t get it all to work smoothly, like you, and needed to spend my time doing other things. Facebook’s documentation isn’t great and their customer service is nonexistent. So So, I’ve always used the $9 Shopify Lite plan which gives you a seamless connection to Facebook Shop, lets you use Shopify’s many payment integrations, plus gives you other selling features – and customer service.
Sorry I couldn’t help with your immediate problem, but the Shopify/Facebook solution works great if you want to check it out further.