If company located outside India, then it's export of service , export is Zero rated supply under GST , so you either pay IGST and claim refund or Submit Letter of Undertaking, subject to conditions for export. ( refer section 2(6) of the IGST Act for defination of export of service) For Invoicing you refer rule 46 of the CGST rules with latest amendments.
Please refer Section 2(6) and Section 16 of IGST Act, 2017 to understand if it qualifies as Export of services. If it qualifies then please take LUT and issue invoice without GST.
Please write mail at Bhavana @ lbkca.in, in case more clarification required.
Thanks Bhavana K L Chartered Accountant L B K & Associates