This is how you publish Dext cost items as Awaiting Payment Bills to Xero after their approval in ApprovalMax:
Select "Invoice" as the Publish To destination (Manage - >Connections ->Integrations):
Select a Payment Method with no stored Bank Account (Lists ->Payment methods):
This is how your cost item should look in Dext:
This is how such published cost items look in ApprovalMax:
Once all approvals have been collected in ApprovalMax, the Bill will be published to Xero as Awaiting Payment: