The only supported iron cluster is with two FE and four Sulphur atoms:
CFE: CYS with an iron sulfur cluster.
HADDOCK will automatically search for closeby CYF residues and created bonds with the iron cluster
The list of supported modified amino acids can be found at: https://milou.science.uu.nl/services/HADDOCK2.2/library.html
You might try to define it as HETATM, but each atom must have a unique name.
Also from your PDB it seems you have multiple occupancies for the iron cluster