That's the flag then, not XAPI refusing. Which is the easier of the two to get out of.
Nothing showed up in Advanced because XO only lights that toggle when all seven of its stop operations are blocked: clean_reboot, clean_shutdown, hard_reboot, hard_shutdown, pause, suspend and shutdown.
Yours has four of them, so the toggle already reads as off and there's nothing to switch off.
Turning it on and then straight back off does clear them, though.
I tried that on a test VM here, on XO 5.205.2. The first click set all seven, the second removed all seven, and suspend was back in allowed-operations.
Your destroy entry is the separate "Protect from accidental deletion" toggle just above it, and that one will show as on. Turning the shutdown one on and off leaves it alone, so keep it if you want it.
If you'd rather not touch the others, this removes just the one key:
xe vm-param-remove uuid=<vm-uuid> param-name=blocked-operations param-key=suspend
I ran that one too, on 8.3, and suspend came back in allowed-operations straight away with the VM still running. What I can't tell you is what set that particular combination on your VM in the first place. Does it ring a bell?
