everyone, I'm setting up a custom gateway for Membership

Hi everyone,

I'm setting up a custom gateway for Membership to include Telma's MVola (a local mobile Money operator) in the payement gateway and they asked me what are:
- the VALIDATION URL
- the CANCELLATION URL
- the NOTIFICATION URL

I've been already spent some time studying the existing payment gateways but I still have no clue about them, and where to find them.

Thanks,