I believe that is a status readout and not settable item. (no soft toggle)
Otherwise this would have been solved a long time ago.
The way to solve this may best lay with a I2C device as was intended for a Pi channel driver that never made it to production.
Raspbery Pi and DMK eng PITA board
But something should be done soon as we will run out of options sometime.
We have been using the same URI sceme based on a sound fob for more than 15 years and that sound fob was not a new thing then.
I use a pc with parallel port interface for signalling so I can use more sound fobs than those using a URI.
But even PC motherboards with PP interfaces have run out as well and I have a supply of them for myself. I’m likely good for as long as I do this. ‘USB printerport’ devices will not work as they cannot be ‘bit banged’ .
But there is this as well.
Or to allow
RPT_KEYED
to be a addressable settable item. Then we can write our own external triggers for it.
I prefer the later. Then the base code is not so ‘dated’.
But to use that event, you have to code a phone tx event (*99) to engage the TXer (COS ). and I don’t think you get a CT with that method, but it’s been a long time since I tried it.