To add or edit a custom field, please do the following:

1. Go to "Advanced Settings > Fields".

2. Select an area where you wish to add custom fields. For example, click the Client tab, then click the Main tab, and then click the Add button.

3. Enter a field name, select a type (text line, number, date, etc). You can also specify a variable for this field (to use this custom field in your templates).

4. Click the OK button.

5. Click the "Confirm Changes" button.