Sometimes PID tuning can fail if using the stock firmware settings. I like to PID tune each heater independently, than re-tune with the other heater at print temp.

Move the nozzle to the center of the bed. I generally have the nozzle about 3mm from the bed surface.

With the hot end at room temperature run M303 H1 P1 S200.

This will PID tune Heater 1(hot end) to 200c at full power(P1).

When it's finished replace the M307 H1 string found in config.g with what's in the console.

Repeat the same steps for the heated using M303 H0 P1 S60.

When it's finished replace the M307 H0 string found in config.g with what's in the console.

Due to the algorithms RRF uses, it's not uncommon for it to take 1-2 hours for the bed to PID tune.