Regarding residue not found in rtp

GROMACS version: 2022
GROMACS modification: Yes/No
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Dear users,
I have added the Co+2 parameters in ffnonbonded.itp, atomtypes, ions.itp and aminoacids.rtp in forcefield amber99sb-ildn but it is still showing the error that residue CO not found in residue topology database. I have also checked the residue name, atom name and atom types correctly. Anybody can suggest me regarding this.

Could you provide more detail on how you setup the parameters (where you got the parameters, exactly what lines were added to which files, how you setup the file, etc)?