is there a "legal" way to pre-populate facebook messenger text box

Question

I'm working on my local e-commerce website that I created using glideapps.com. And I have removed the "buy" button from my product's page and replaced it with a "message seller" button. The reason i did this is because my shop is entirely local. I want my customers to message me first, set up a plan for them to come pick the product up. Anyway, on the website when the customer clicks on the "message seller" button, it will redirect them to my facebook page's messenger. The hyperlink for that button is https://www.messenger.com/t/**MY_PAGE_ID**. As you can see, this is a static url. Meaning when they click on it to reach me, i would have no idea what product they were interested in. I would have to ask them what SKU # were they looking at and from there we can plan. I googled it to see if there was a way to manipulate the URL and make it so that when you click on the "message seller" button it will redirect you to messenger with prefilled text that contains the SKU# of the product you were looking at. for instance "Hey there, is SKU123343 still available", you get the idea. And each products would have a different URL based on its SKU#. I was hoping this would work but i read that pre-filled text is against facebook terms and conditions. But i really need a way to get around this. Any ideas or workarounds?

FYI-- I have been looking for other alternatives like using SMS or whatsapp, or even creating a 1v1 chat inside the glideapp. But i disregarded those because 1) SMS means i would be charged for texts. 2) no one uses whatsapp in my community, facebook messenger is all they use, 3) 1V1 chat means i would get a lot of spams and non-trusty customers.

So if you can suggest me an alternative way I would be very grateful. Im still begginer with coding but i will do what it takes for this to be automated!