Getting GPIO4 to work

Greetings all!
I’ve got an RPi3b+ running ASL 1.01 with a BRIAN as the radio interface. It’s a CM108 sound card based system, so I’m expecting the GPIO functions to work. After lots of searching, I’ve not come up with a way to automate the toggling of this signal. The instructions from the author of the project tell me to add (amongst other lines and settings) the following lines to my rpt.conf file

[eventsXXXXX] <- replace XXXXX with ASL node number
cop,62,GPIO4:1 = c|t|RPT_RXKEYED
cop,62,GPIO4:0 = c|f|RPT_RXKEYED

If I turn on the rpt debug I can see each of these events getting fired as expected, however the GPIO4 pin does not change state.

From the asterisk console a:

rpt cmd XXXXX cop 62 GPIO4=1

will cause the GPIO4 pin to assert and:

rpt cmd XXXXX cop 62 GPIO4=0

will negate that assertion. Notice the “=” in the command. That works every time. A “:” does not as indicated in the guidance for the event stanza. The above rpt cmd tests validates the physical and logical parts are working. So why does it not work in ASL? I suspect the author of the BRIAN (and all those indicating this event method works) are using Hamvoip distribution and there is some “special sauce” in the app_rpt.c code to accept that “:” in the event command and make it work. So, how does one actually toggle the GPIO pins like the example above on ASL? Thanks in advance.