Why can't I tag products on Instagram after using Shopify?

Hi, I am having such a problem tagging products on instagram and yes, I do know how to tag them normally.

I wasn’t using Shopify and recently I started using it. I connected my FB shop and Instagram shop successfully. I can tag products to a post AFTER it’s been posted ONLY on FB and not on Instagram. Instagram continues to show the message saying that my web domain does not match. I spent countless hours with tedious and terribly ignorant Meta Concierge Support people who just repeated the same thing asking for a number of IDs on separate occasions then they sent me a message saying they scheduled a call but no one called as I waited here at the agreed upon time. I’m so fed up with them and feel desperate. Please help.