Gromacs errors for terminal group selction

GROMACS version:
GROMACS modification: Yes/No
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Fatal error:
Atom NH3 in residue MET 1 was not found in rtp entry MET with 18 atoms
while sorting atoms.
. I am facing this error while generating the .gro file

What was the exact command you used? Which force field are you working with? Note that the terminal -NH3 group might not be supported in your chosen force field.

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