How to index a tenancy?

As soon as the signature date is entered, the system automatically returns the value of the starting index, so after entering the rent price the values of “Base rent price” and “Current rental price” will be set up to date.
And on the anniversary of the tenancy the button 'Apply the current index ' appears and does not disappear until you click on it.

The system automatically generates an email proposal to send to the tenant and a price difference invoice if the call for rent for the current month has already been generated.

After sending the email notification to the tenant, the system updates the tenancy index.