To run a bill, you need to go through the following screens under the Tools menu in this order:

Meter Validation screen
First step is to validate the data that you are going to run a bill on.
Meters log various events that can cause the data to become invalid, such as a Tamper event or Reverse Run.
When the systems reads a meter and an invalidating event comes in, all the data for that period is also marked as invalid.
The validation screen deals with validating data.
You can get more information about validation here.
Run Bill
Next is to just run the bill.
Bill Variance Report
Compare previous 3 bill runs with this bill run, and highlights outliers.
This screen is best opened from the bottom of the Run Bill screen.
Maintain Bills
View and Delete bills.
Bill Export
Export the bill in a format that your system uses.

VAT

if you want to run with 14% vat, please check 'Enter Separate Invoice Date (optional)' and enter a date before 1 April 2018

Tariffs that are not validated have undefined behavior and often revert to 14% VAT