SGST Invoice on a National Political Party

Hi Team
One of my friends is engaged in Data Entry Job for a leading national political party office with expected turnover of Rs.10 lacs p.a. He is having GSTN with operation confined to only one state.
1. Should he create Invoice with/without GST i.e. IGST
2. If the party declines to pay the Tax,what should be the treatment of the GST