I tried a lot of different ways, for the reverb effect I can access each property like this:
But that doesn't work for some properties of the delay effect.
According to the doc, most properties names on AudioEffectDelay contain /, which means they can't be directly written. They need to be accessed using get and set: https://docs.godotengine.org/en/3.0/classes/class_audioeffectdelay.html#class-audioeffectdelay
For delay_ms, it would be:
Thank you so much!!!