As far as I am aware, one can only advertise Products that are in stock on Google merchant center. Print on Demand is again their term, unlikely you will find such app.
Read it up here:
I hope I've answered your question!
I had watched a shopify video showing how to set up a store and of course i chose that app. I bought the images and uploaded onto my store all to find out later it won't get approved by google merchant center because this images are not considered real. google calls it dummy images/placeholder images. going on 6 weeks of setting up the store and finding out i won't beable to get approved to advertise with google. discouraging.
Yeah, I get your point. Unfortunately, those are the Google's policies.
As @Nick_Marketing mentioned, print on demand is not allowed. Reference: https://support.google.com/merchants/answer/6150127#:~:text=Unavailable%20promotions
The only way you can move forward is to maybe limit your products, and stock these products. Then comply with Google's requirements, here is a basic list: https://community.shopify.com/c/Ecommerce-Marketing/Checklist-Suspended-Google-Merchant-Center-Accou...