gcloud deploy ... --trigger-resource for triggering on Firestore write 'CloudEvents' needs a bit of clarification - google-cloud-firestore

Question

I read and followed the examples found on Google Cloud Firestore Triggers. I have been able to deploy these examples following.
gcloud functions deploy my-second-event \
--entry-point CloudEventFunction2.Function \
--runtime dotnet3 \
--trigger-event "providers/cloud.firestore/eventTypes/document.create" \
--trigger-resource "projects/my-projectId/databases/(default)/documents/messages/{pushId}" \
NOTE that the /documents/messages/{pushId} part of this resource aligns with the "Deploy your function" section.
HOWEVER a little further down --trigger-resource 'NAME' is described as...
The fully qualified database path to which the function will listen. This should conform to the following format: "projects/YOUR_PROJECT_ID/databases/(default)/documents/PATH" The {pushId} text is a wildcard parameter described above in Specifying the document path.*
Now we get to my confusion when we follow the link to "Specifying the document path". I believe I understand what is meant by "Functions only respond to document changes, and cannot monitor specific fields or collections.". HOWEVER if we look at the above /documents/messages/{pushId} - 'documents' is a collection and 'messages' is a document. Following from the above limitations about functions only responding to document changes, I would NOT expect the event to be triggered by the {pushId} event (because the pushId is EITHER a collection or a field (it sits directly on a document 'messages').
What seems to be to be indicated is that the {pushId} wild card be put directly under the collection 'documents'; resulting in...
--trigger-resource "projects/my-projectId/databases/(default)/documents/{pushId}"
Meaning that when a new message is pushed to the documents collection the cloud event is triggered.
However the above change yeilds below...
ERROR: (gcloud.functions.deploy) ResponseError: status=[400], code=[Ok], message=[
The request has errors
Problems:
event_trigger:
Expected value {pushId} to match regular expression [^/]+/[^/]+(/[^/]+/[^/]+)*
]
While I am sure I am doing something wrong, I am struggling to make sense out of the above observations, also my function is not being triggered.
I would really appreciate any hints as to how this is to be understood, and or at least how to get my function to trigger on create.
FYI; the 'Function' I am using is from the dotnet template provided by Visual Studio (2022).

Answer 1

I am late to the party, but if the collection in your database is literally named documents then your path is going to look like this:
--trigger-resource "projects/my-projectId/databases/(default)/documents/documents/{pushId}"
The second instance of documents is the literal name of the collection you are watching.