Guidance needed on filtered record collection using URL placeholder

Hi, I am a new user looking for advice on this issue:

I have a master-detail (1:many) data source. I can get the master record collection to show in a list without problem. The child record collection needs to be dynamically filtered using the master record id (that means it has to be reloaded depending on the selection of the master record). To do the filter I use a URL placeholder in the data source URL. It tests out ok with static sample master record Id.

For display and navigation there are two pages, the master page and the detail page. So on the master list item event “Component tap”, I add a “Get record collection” action, and assign the master “current.Id” to the child record collection URL placeholder, then open the child page with its own list items.

For some reason the child record collection is empty. I have not been able to find the cause but suspect the URL placeholder is not working. If you can see where my mistake is please
advise. Or please point me to any good literature or youtube tutorial on the subject.

I have found a nice work around in the “collapsible grouped icon list”, without the need to do filtering on the child record collection. But I would still like to understand why my original approach did not work.

Thanks in advice!

Okay I have finally figured out by myself how to use REST API data source containing a URL placeholder, after trial-and-error. Thanks to anyone who thought about helping but didn’t quite understand my question.