How to make requests from the site to viber/telegram/ as a last resort e-mail?

Question

Messengers

Introductory:
There is a site catalog, which hosts about 30 clients. All customers have their own products. The user can order a callback (in this case, a call order with the user's phone number (if he specified it) and the page from which the order was made is sent to one general mail, the manager looks at who the call order was addressed to, calls the client and informs about the call order from site - the scheme is nonsense).
The bottom line is that the site can send requests for a callback to the messenger (telegram or viber) to customers. Those. we will indicate his phone number in the client’s product card, the client sets a certain messenger for himself. And when on the product page of a certain client they clicked "order a callback", it was this client who received a request for a callback.
Somehow it turned out chaotically, but I think the idea is generally clear.
Maybe someone has come across a similar problem and can suggest a ready-made solution, or at least in which direction to dig.