MattS-UK:
There is no mention of the ':' terminator in the documentation you quoted.
The documentation states the key/value is terminated by an end of line character.
So, which is it?
I know, and that's also the reason why at the beginning I lost many hours trying to understand what was wrong. Then by using a serial logger and browing the ProSim forum I learned every string was followed by a ":". Actually if I log the serial traffic this character is there.