Lesser inward Remitance for an export Invoice - Goods and Services Tax - GST

What should be done if the inward remittance received is less than the invoice amount raised for the export of services? Additionally, if a third-party processor fee is charged for remitting the payment, will this affect the amount to be received under the filed LUT for without payment of tax (GST)? Is there any interest payable under GST, or can the fee be shown with the receipt of the remittance receipt as supporting documentation? For example, if the invoice is $1,000, but the fee is $100, resulting in $900 being remitted to the bank and reflected in the FIRC, what should be done about the $100 that was not received? Does the requirement to receive the full invoice amount within one year apply to the $100 shortfall in this case?