I have got Commissions from Booking.com which is not registered in India. Hence, had raised Invoice and chrged IGST @ 18% on Commissions. 

While filing Gstr1, the same was showed under 6A-Export Invoices. I have got a mail from the system which says that 

Invoices not transmitted to ICEGATE because of Negative ledger balance.
 
Can someone please guide on the same