The user could be from a country where paying to receive phone-calls is unknown. From some brief Wikipedia research, this is only a common model in the USA, Can

The user could be from a country where paying to receive phone-calls is unknown. From some brief Wikipedia research, this is only a common model in the USA, Canada, Hong Kong and Singapore (https://en.wikipedia.org/wiki/Receiving_party_pays https://en.wikipedia.org/wiki/Receiving_party_pays)