If any of your invoices have an associated Import Declaration Number, please add the number, in brackets, to the end of the invoice reference.
For example, your invoice reference is Noodle Order, and the Import Declaration Number associated with that invoice is B12345678. You would edit your invoice reference to become Noodle Order (B12345678).
To do this in Xero, go to Accounts>Purchases>New Bill. Under Reference, you can insert the invoice number and import declaration number in the bracket:
For more info on how to obtain the import declaration number or procedure on importation, Kastam (or Royal Malaysia Custom Department) has an extensive guide inside their portal. You may refer HERE.