Good engagement, no conversions

There are many reasons why this could be happening.

During your PPE ad phase, did you get any conversions? (Either VC or ATC)

Once we know this I'll lay out a couple of possible reasons.

Change of messaging can work. Also redesign your landing page. Place content that attracts and convert. Also, check for the bounce rate. If that is on the higher side, think of re-targeting your ad.

Without taking a look at the site it's hard to say. Have you got hotjar or some similar tracking installed on the site so you can get a more detailed look at what visitors are doing on your site?

Why dont you use sales funnel to maximize your conversation rates?

Setup a attractive landing page. Add high quality message that's can visitor/buyer are feel safe secure and sanctification. If you can't do so you want to hire a web developer to make your landing page.

Thanks

What is that initial offer?

Best funnel arrangement I've seen for ecommerce is a special landing page offering a super deal on an item someone in that niche will definitely want, at a great price. This is either a loss leader or a breakeven price point for you. Understanding your Cost of Customer Acquisition is important here.

An example is in the barbecue niche. It's a big step to go from not knowing you and your site to buying the $500 barbecue, so the initial offer is for a heat-resistant cooking pad that sits on the barbecue rack.

Immediately following their entering credit card info for that nice offer, you offer them a one-click upsell to a second item. This one you price at a regular margin so you can make some money. It's easy to buy and it makes sense. In the barbecue case maybe it's a spatula set or an apron.

Now you've gotten a buyer and you get them on your list and start marketing them the other things around the anchor product (the barbecue).

I suspect an issue is you're concentrating on one product--the t-shirt--and what else is there to buy in that case? If that's so, you need more breadth to your offering to use the above strategy.

And remember that t-shirts are vanity items with limited utility. There's a Lovecraftian "Miskatonic University 1930-1 Arctic Expedition" t-shirt I like, but I don't think I'm ever actually going to buy it.