[AlphaCommerceHub] Why does a manual 3D-secured `AuthPayment` request through the API Explorer with the default data fail with the message «Invalid Parameters - order.xid: Maximum length is 20»?

I did not change anything in the API Explorer, just used the default (prefilled) data.
The «API Integration Guide» does not mention any limitations on the XID param:

For comparison, here is the XID parameter specification of another Australian payment service provider (SecurePay): [SecurePay] What is «3D_XID» in a 3D Secure authentication scenario?

I have got an answer from the AlphaCommerceHub support:

I’ve escalated this to the team to troubleshoot.