Airwallex invoices allow you to upload supporting documents. This is because depending on the transaction, supporting documents may be required to validate the payment.
For example, the Chinese government has very strict rules around financial transactions inbound and outbound of China and requires documentation to prove the legitimacy of the transactions. For more information around why this is the case and what you may need to provide, please read this FAQ.
There may be other instances where documents are required irrespective of whether you are trading with China - for example, if the transaction is very large - in which case you will be notified by one of our Account Managers directly via phone and/or email.
As always, if you have any questions on this topic, please email our Customer Support Team at email@example.com.