1) When creating or editing a matter, turn on "Evergreen Retainer".
2) Enter the amount of retainer you wish to maintain for this case.
3) Turn on "Add Retainer to Invoice".
4) Save the matter.
What Happens Now
When your invoice reduces the available retainer below the desired Evergreen Amount, a new item called "Retainer" will appear in the sub total section, requesting the necessary retainer payment.
Note: When the invoice gets paid, the retainer portion of the invoice will be added as credit into the client's "Operating Account". If you'd like this to be in the trust, simply transfer the funds by following this guide.
Pro Tip: Make sure the status of the matter you're billing is set to "Open". If the status is set to "Pending" or "Closed", the retainer will not be added to the invoice.