This article explains how you can add service sub-type. 

How to Add Sub-Type(s) of Services:

A. In the Settings tab, navigate to Billing Setup and click on Add Service Sub-Type.

B. Select the treatment type from the drop-down menu. 

C. Select the type of service, i.e. billable and non-billable. 

D. Select the service for which you would like to create a sub-type from the drop-down menu. 

E. Click on "Add Service Sub Type", enter the description for the service sub type and click on save. 

F. To keep the status of the sub-type as active/inactive toggle the button under the Status Column. 

G. To edit the sub-type, click on the pen-paper icon and edit the description of the service. 

H. To delete the sub-type, click on the trash icon located under the action column. 

Note: You would need to be careful while deleting these sub-types as it may construe some reports.