How can I enable users to select payment methods in expense reports?

You must set the option, Enable Payment Method, to Yes. If you don't want to allow users to select the payment method for reimbursement of each expense report, set the option to No.

By default, this option is set to No. The application uses the default payment method, such as check or EFT, that was set up for the users' reimbursement. You can optionally set the option at the implementation level on the Manage Expenses System Options page, which applies to all business units. Alternatively, you can specify exceptions for specific business units in the Create System Options: Specific Business Unit dialog box.