Tax Invoice when goods sent on approval basis :
Notwithstanding anything contained in sub-section (1), where the goods being sent or taken on approval for sale or return are removed before the supply takes place, the invoice shall be issued before or at the time of supply or six months from the date of removal, whichever is earlier – section 31(7) of CGST Act.
Thus, tax invoice must be issued within six months from removal.
Bill of Supply may be issued at the time of removal of goods.