Hi Clément,
It seems that Make currently doesn’t support filtering by a rollup property, which is the reason for the error.
So, one solution option is to use the “Make an API call” Notion module and call the “Query a database” endpoint, constructing your own filter body using the Rollup filter data structure you can find here.
Then, you can use an Iterator module to loop through the Results array.
I tried the “Make an API call” module but I can’t find the members linked to the event as you can see on the screenshots. Do you have an idea of where I’m wrong ?
It looks like “Event invités” is not a text property but it outputs pages. You could try using another property of formula type that uses the “format()” function to turn those into text, and then filter by that new property