Some stores require to add default service charge in their tickets. Following steps will help you to add default gratuity.
Back office–> admin–> store configuration–> charges–>add service charge percentage–> press ok to save.
Now, select the order type where you want to have this default service charge to be added.
back office–> order type–> select order type–> edit–> select the service charge applicable option –> press ok to save and restart the POS.
Now if you take order in that selected order type, the service charge will be added automatically.