It's been a while since I've looked at that stuff but I'd think that the IsInside:true would be picked up by the default BI ONVIF trigger at the end of the list under the ONVIF Config button that says RuleEngine/FieldDetector/ObjectsInside with Attribute IsInside="true"
Is there a green check mark next to that line and profiles right as appropriate for whatever is active?
What does the BI log file show when you activate that cam/trigger? If it's picking up the ONVIF event/trigger, then it should show something like:
0 6/1/2024 12:12:54.397 AM CAMERA_NAME ONVIF Event: RuleEngine/FieldDetector/ObjectsInside (IsInside="true")
What control do you have over the rules in the Amcret cam? Can you name them? If so, then try naming it and then creating a new BI ONVIF "Listen for: line and in the Contains put that name with action Trigger.