i want to connect my firebase database with my onesignal app. 

i want whenever a new document is created in the sub collection of my database it sould trigger.

but i don’t know how to write structured query to do this. i am new to it please help me.

here are some screenshots of my database:

can i listen to this message sub collection whenever new document is created if yes then how can i write the query for it.

i got stuck here: