It sends one. The PLC clears request on a timer without waiting for it.

Then ask the authors to draw what acceptance should do before choosing a longer timer; it needs to work when the application is slower than expected too.

Who wrote the current interface? They should help explain the timer.

Two contractors. Each thought the other had written the sequence description.

I'd sit both down with one missed request. I don't know their intended protocol, but the empty space between their documents is now your support workload. It needs an owner beyond commissioning

Have either of them supplied the acceptance and clearing sequence since you asked?

Only a list of signal names so far. Still asking for the sequence.