Please don't test your biller setup with NATS4 MerlinBill's test account—it won't work correctly.
This biller does not return to the NATS cascade.
Setting up on MerlinBill Site
Before you can configure MerlinBill in NATS, you must first sign up for a merchant account with them. Go to MerlinBill website, signup for an account, create the join options you intend to use MerlinBill with, and copy the product codes that are given to you.
Find the password script location and set it to: http://linkdomain/signup/passwd_mbill.php
After that find the return URL location and set it to: http://linkdomain/signup/returnurl_mbill.php
When setting your returnurl_mbill.php path within MerlinBill website, you must also append ?key=[KEY] to the end of your URL.
For both examples, simply replace "linkdomain" with the linkdomain to your site.
Setting up MerlinBill in NATS
Fill in the Account Number, Username, and Password that you received from MerlinBill when prompted, and click Save. If you were not provided with the necessary information, please contact MerlinBill.
Set up a join option for each site you wish to configure, and fill in your MerlinBill product code in the "MBILL(id:x) Product Code" field (this product code must be obtained directly from MerlinBill).