How to fix this?

GROMACS version: version 2023.3-Ubuntu_2023.3
GROMACS modification: Yes/No
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Fatal error:
Residue 156 named SER of a molecule in the input file was mapped
to an entry in the topology database, but the atom OG used in
that entry is not found in the input file. Perhaps your atom
and/or residue naming needs to be fixed.

Tried using all the force fields, but met with same error.
PDB ID: 966C