Thanks I think I'm beginning to understand. I thought I needed to add an alternative code (T=1 afet T=0) after each command, but with the same command.
I have found a "non event code" that seems to work, and if I add it after each single command (with T=0) it seems to do what it should.

I'm still struggling with commands that should be consecutive. For instance channel 21 is digit 2 and then digit 1 in a row. Using the zero event code creates a problem here.

One question though regarding Makehex that I have installed. It does not seem to generate the right code for me. I select
protocol = rc5
device / main a = 21
then it generates a file that says at header level device is 21, but at line level it says device = 15?
Did I miss something?

Thanks again for your valuable help.

PS: regarding the 0.5 second limitation it does not seem to be linked to using a phone as a remote, but rather to my receiver as I don't have this delay on other devices.