new required field in one page shoping and register user

[Bambosz]

 

Mayby anyone here could help me. Can't find answer on my problem.

I need to add additional required checkbox in fast shooping and register new customer in presta shop [1.6.1.6] (RODO etc.)
Insert new checbox in code is simple, but cant find out how to make it "required" (customer must allow to use his data befor make new purchase).
I know there is a plugin for that byt my friend (shop owner) don't want buy it :/

I was try to insert it at the begining, where name, adress, phone is, but don't know how to set that new field as required and how to "validate it".

Mayby you know, or maybe you saw any post / article about adding new fields do one page shooping and register ?

Best regards from poland ;]