Flat mount is flat mount, generally road use but there are MTB things, mainly XC that have started to use it, post mount is what you've bought, you can just swap the caliper. There are flat mount to post mount adapters (search that) but they're ugly.
Flat mount is flat mount, generally road use but there are MTB things, mainly XC that have started to use it, post mount is what you've bought, you can just swap the caliper. There are flat mount to post mount adapters (search that) but they're ugly.