Ted here from Shopify, thanks for reaching out to us!
After you pay your first subscription fee to Shopify, you might be eligible for a Google Ads credit. Only Google Ads accounts with no activity history are eligible for the Google Ads credit. When you sign up for a Google Ads account by using the Google Shopping app, you can then qualify for a Google Ads credit automatically by spending a specified minimum amount in the first 30 days. More information can be found here if you would like to take a look.
Please let me know how you get on with this and if you are unable to avail the credit even though you've met the requirements (as mentioned in the guide above) I'm happy to take a closer look.
Thanks a mill,