This is part of the problem. We set people up for failure in this regard across a lot of clients, not just zap.stream. That said, I believe Zap.stream gives you an initial credit to allow streaming for free to get you started. I don't remember the amount of time span. 

 Oh I think nostr:nprofile1qqsxua0hju3e0j3jjhs0fjs0h3htnnreh6zm4lw4d0fhsgsv4rhwwnsprdmhxue69uhhyetvv9ujumn0wd68yurvv438xtnrdakj7qg4waehxw309aex2mrp0yhxgctdw4eju6t09uq3camnwvaz7tmwdaehgun9d3shjtnev4nksun09eekjar99ujwapd9 has a guide for streaming perhaps?