As of version 3.1.0 , the configuration files for the Payment Importer are located in the Database and not the client.
If this is an upgrade to 3.1.0, please see the information in the 3.1.0 Upgrade article.
In order to see the database for Payment Importer, go to the RTLImport database and
SELECT connectionstring FROM rpscontrol
If this needs to be updated, correct it using SSMS. The connection string needs to be in the following format
Data Source=[Server Name];Initial Catalog=[Tax Database Name];User ID=[UserID];Password=[Password]
Example on sqldev01 (Without username and password):
Data Source=sqldev01;Initial Catalog=Smithclone2;User ID=[UserID];Password=[Password]