Why is "Dia membayar makanan dia" not accepted?
I believe it has to do with the suffix "-nya" which would denote possessing from the subject of the sentence?
Hmmm... that's not really an answer... You are just stating that "Dia membayar makanannya" is correct. Like Hakkon388572, I also wonder why "Dia membayar makanan dia" is not accepted.
Why not: Dia membayar untuk/buat makanannya?