Gst liable or not on this payment?

I hope, you are not a regiostered person.

Export supply is subject to Interstate supply...

Interstate supplier is fully liable to get registration under gst. So you have take registration of GST.......

There is 2 type of provision for export supplier.....

1) Pay IGST from your own pockets... and then apply for refund.........

2) Don't pay IGST make bond or letter of undertaking.. After that bank will give Bank Guarantee.....

According to section 16 of IGST ACT. The Export supply is subject to zero rated supply...........

So you should mention it in GSTR 3B in 3.1 (b) Outward Taxable supply (zero rated)................

same shall be shown in GSTR 1 in 10 Exports Invoices...........