heya,
it is explained in the documentation that this is not supported, but that does not mean you cannot do it. it means I will not add support for individual store plugins because there are way too many of them.
The Raidable Bases plugin has its own built-in cost system for purchasing and spawning bases using the /buyraid command.
Store plugins also have their own pricing and cost handling. If they do not have an option to have listings without a cost then it will become a problem.
If you set a cost in a store plugin, players will be charged twice: once by the store, and again by RB (unless you specify free in the command)
If the base fails to spawn, the store plugin cannot issue a refund—RB will refund charges made with the buyraid command only (which can be used in chat and rcon).
You have a few options:
Have players use the /buyraid command to buy raids, as intended.
Set the price only in the RB plugin to avoid double charges and refund issues, not in the store. This is your best store option.
You can specify free in the buyraid command, and handle it through the store, but if the base fails to spawn then it is your responsibility to refund the player any store credits. This is not advised.
buyraid 0 steamid
optionally, buyraid 0 steamid free
0 is the Difficulty Level in the profile. so that would be for an easy raid.
steamid is whatever the store plugin uses. ServerRewards uses $player.id