This is what just worked for me. Hope this helps:
I had to add my billing info into Google Ads. Then return to my Shopify dashboard.
Click Google under your sales channels
Click Settings then scroll down to Google Ads account. There’s a button to confirm you have added billing info to your Ads account settings. Confirm you have.
When I returned to view my products on the sales channel, the message no longer displays.
Thank you! Worked for me as well. In Google Ads (https://ads.google.com/) itself I had a quite prominent alert telling me this as well. See the image, it says "No ads will be delivered for your account Enter payment information so your ads can be delivered."
Fixed it, waiting for final confirmation of my payment data, but the message in Shopify has been gone after I confirmed as you described it.