How to add SMS confirmation?

Question

Computer networks

Hello. The developer has a website with its facilities. You need to add the function of booking an apartment. To prevent malefactors (schoolchildren) from booking all apartments every day, we decided to add the function of confirming this reservation by SMS. The user receives an SMS with a code, he enters it, the reservation is confirmed. But how to add this SMS confirmation function, I have no idea. Tell me something about this. Is it free or are there fees?

Answer 1

How to confirm registration via SMS?