Synch eos rp and flash speedlite 430exII, godox x1t 2.4g

If you want to control the 430EX II via radio, you need to connect a compatible radio receiver to the hot foot of the flash. The only wireless capability the 430EX II has own its own is optical wireless control using Canon's optical wireless protocol.

The Godox X1R-C is the only radio receiver not built into a Godox flash that I'm aware of that is compatible with all of Godox's 2.4GHz transmitters, such as your X1T-C.