I know many, many if us have Wix website and are struggling finding the product ID. Here is how I found it and I was able to update my catalogue which fixed my tag health.
After logging in you will see your dashboard user dashboard you should see CONTENT MANAGER. Once you click on it, It will open in to MY COLLECTIONS. If you hover over the blank box with the + it will tell you, you cannot edit it unless you are are editor.. Click on the link to bring you to editor. Once editor opens you will see the tab to your left that says PAGE CODE> Content Manager. Scroll down until you see variants, click on it. It will open back up in the dashboard. If you see to the top-right there are three dots next to new product. Click on the three dots. It will allow you to download it as a spreadsheet.
Here is what I did to add it to my catalog. Go to Pinterest Ad>Catalog. Click the down error that will "expand". Over over report status and you will see a download data source. I downloaded it, added the Product ID to my items. Created my URL and uploaded it as a new data source and Pinterest will add the missing info.