You need to specify a bank account under Payment Methods in Dext if you want your cost items to go through a predefined approval process in ApprovalMax and get published as Paid in Xero once approved.
This is how it works:
Create a Bank Account in Xero (or make sure you have one):
Find your account in the Chart of Accounts in Xero, click on it and assign the account code for this Bank Account:
Sync the data to ApprovalMax:
Synchronise the data to Dext by overwriting the integration (change the integration and select the same one from the Integrations page):
Now, the Bank Account should become visible so that you can assign it to a Payment Method. To do so, open Payment Methods in Dext, add a new one or assign your Xero Bank Account to an existing one: