When you create virtual cards, you can input any data that you like into additional fields. This data is entered as name:value pairs. This data is exclusively for your use for any purpose. For example if you want to keep information on which client you want to pay using the created cards, you can enter custom data in the form: Name: Client, Value: Acme Company.
You can add more entries using the Add Additional Details link. You can delete unneeded entries using the delete icon to the right of the field. You can have a maximum of 20 entries in the additional details section. Your installation may have some entries pre-filled with default values and some of them mandatory. Mandatory entries have a darker background and cannot be deleted.