Add a feature to manage Jet_Booking_Units_Manager

[dgentrepreneurtajul]

In the Apartment Booking system has the option to add Units to increase the booking amount. By default, its value is 1.

** In the booking system, I want to add the unit item by the front-end form. It will maintain a seller by their user ID.

• So please, add a feature about adding the unit value by using the front-end form or by adding metadata!

[dgentrepreneurtajul]

It will help us to use the booking system seamlessly.