Hey all,
I think what I'm trying to do is relatively simple but so far it's not working sadly. I have the following Sharepoint List with these 2 columns that I would like to have added to a collection in my Power App:

In my Power App I have the following formula on my OnStart property:

ClearCollect(DocumentNumberCollection, ShowColumns('Authorization Matrix', "DocReference", "SequentialNumber"));
This is the only way I won't get errors. However, my collection remains empty sadly:

From the examples online I tried it without the single quotes:

But then it complains that "Name isn't valid. 'AuthorizationMatrix' isn't recognized"
I tried adding the spaces:

Then it will complain about that DocumentNumberCollection isn't recognized and another error on the first argument of ShowColumns.
What am I doing wrong?