Custom fields are used for storing additional attributes that supplement standard PortaBilling information. This can be information about a customer’s bonus, driving license ID, or a code name that maps an Internet customer to a certain vendor, etc. This can also be very useful for troubleshooting. Create your own custom fields and give them whatever name you like, set a field type and then control their visibility, etc.
Custom fields are treated like any other field; you can organize them via customer classes and fine-tune their visibility for end users. Then desired custom fields can be set on the Customer/Account Info page and used for search queries.
Custom fields are added to Invoice templates under the Header section and it is possible, as well, to add custom fields in Layout Designer (right-click → Header).
This functionality allows you to manage extra user information that in its turn facilitates customer support and helps with troubleshooting.