Why can't I modify the code on my website to display payment options?

I have been trying to add a “we accept credit cards, Paypal, & Apple pay” under the “buy” button on all of our product pages. Whenever i go into the code section “liquid” and add a simple html code so I have this one line of text, nothing changes. Is there a reason that shopify makes it so hard for anyone to make simple changes to their website? I have hired a “shopify expert” but honestly I just want to do it myself but it seems that Shopify is built so you can’t do so. Can anyone help me??