The Payment method field in the invoice editor is a drop down list that only contains certain values. Can you add an enum like the following to the property in the JSON schema to help document what the valid values are?
I'm assuming these values are hard coded? Or, are they stored in a table somewhere? There is a payment methods table in the fees/fines module, but, the values are slightly different.
The same change needs to be made to organization.json in the organizations module.