TY for your answer @Anonymous!
I’m writing so late because I try your recommendation since u wrote.^^
The usual connection fields are SOL.“Document Type” = SO.“Document Type” AND SOL.”Document No.” = SO.”No.”. Most of them doesn’t exist in the field list for the table in the conector...
The ; is there instead of a comma because it is a German environment.
I tried around and current I have found this:
I don’t know even if those are the right fields, but it seems good so far.

So far I see this come because Business Central can’t use the delegation and the usual workaround is to load the data to a collection, but here we have the same problem that we have to define documentId…

For this I don’t find a workaround, even the problem seems basic. Getting data from header/lines tables which are provided by a connector which doesn’t support delegation.
Do you or another reader know what is to do next?