According to the online manual, you can not give the keyword agruments "p3" or "p1". That's the problem. You need instead to use only the keyword argument "projections", which may be a list of projections:
p1 = Projection(atoms=[Boron], l_quantum_numbers=[0, 1, 2])+Projection(atoms=[Carbon], l_quantum_numbers=[0, 1, 2])+Projection(atoms=[Nitrogen], l_quantum_numbers=[0, 1, 2])
p3 = Projection(spin=Spin.Up)
fat_bandstructure = FatBandstructure(
configuration= configuration,
route=['G', 'K', 'M'],
points_per_segment=200,
bands_above_fermi_level=All,
projections=[p3,p1], # a list of the projections defined above
)