Canon EOS RP Instruction Manual page 777

Using flash in < f > or < d > mode lowers the shutter speed.
Under [ z : External Speedlite control], set [Slow synchro] to [1/180-
z
1/60sec. auto] or [1/180 sec. (fixed)] ( = 224).
The flash does not fire.
Make sure the flash is securely attached to the camera.
z
The flash always fires at full output.
Flash units other than EL/EX series Speedlites used in autoflash mode
z
always fire at full output ( = 221).
When the flash Custom Function setting for [Flash metering mode] is
z
set to [TTL] (autoflash), the flash will always fire at full output ( = 230).
Flash exposure compensation cannot be set.
If flash exposure compensation is already set with the Speedlite, flash
z
exposure compensation cannot be set with the camera. When the
external Speedlite's flash exposure compensation is canceled (set to 0),
flash exposure compensation can be set with the camera.
Troubleshooting
569