Reference field referring to a different table for field xxxx

Dear Experts,

In a scenario, I have to join A071 (Article Per site) and KONP (Conditions Item) tables.

I created a DB Lookup exp for KONP with KNUMH referring to the result of another DBLookup for A071.

The result of this is to be stored in KBETR field in KONP.

Have a look at the error generated here-
https://weblogs.sdn.sap.com/weblogs/images/252055257/DBLOOKUP_err1.jpg

The error generated is

Reference field referring to a different table for field KBETR

Where am I going wrong? I tried to create a structure as result of the table. But the error persists.

Please help in finding a solution.