My Google merchant account keeps giving me error messages and will not let me connect my Shopify to my YouTube channel. I haven’t found where or how to fix this and Google is no help at all. I talked to someone who wanted $3500 to fix it–surely this is a common problem you guys have help articles on? I can’t even get the store set up to make that first sale. 
Hey @ShirleyJump , thanks for your question.
I’ll be honest the only experience I have with Google Merchant Center is in setting it up with a woocommerce store but here’s a video I found on how to set it up: https://youtu.be/m85kfIWhhoc?si=9H06BZo3uma2Ncft
My recommendation to you is to run through the set up process again, you probably missed something.
Now if that doesn’t work, send me a reply here along with your error message and some screenshots of what you have tried so far.
I don’t have much experience dealing with Google Merchant center and Shopify but I’ll do my best to help.