Hi,
As far as I can see, each external event triggers the webhook as an independent execution and between each execution they have no access to and about each other. so the normal outcome is that it sends 20 individual messages.
There might be other ways but IMHO you need external storage to store state
Something like this:
Webhook call X is triggered y times → writes into a file or DB , this event , this time has happened
An additional WF or trigger detects (new file or new rows in DB:
get triggered. waits Z amount of time (you define this) and after that it reads all the events that happened between the first one and the wait time and send one message out with all the events.
this allows for the events to be combined and you have still all the original data about when and what.
regards,
J.