You may want to look at alternative choices for partitioning the molecule into fragments. This is stretching my knowledge of inorganic chemistry, but I think the Ni electrons live in d orbitals that interact with both of the rings. Thus, it’s not appropriate to associate the Ni with one ring but not the other, as you’ve done in your input file. I think this is why you are having trouble converging the SCF procedure for the monomer.
I think your best option is intramolecular SAPT, which will use a more rigorous approach to localize orbitals to particular functional groups. You should use the input format described here in which you specify the charge & multiplicity of the entire molecule first and then specify charge & multiplicity of each fragment.
You will still have to make a choice about how to partition the molecule into fragments. It is usually recommended to avoid cutting fragments across bonds with pi character and to avoid having a single atom by itself, but I don’t know if transition metals are an exception. Maybe @dasirianni can weigh in.
In any case, after running fsapt.py, you should check the “Orbital Check” section of the output. If any value is bigger than 0.1, then you’ve made a poor choice in partitioning the molecule.