Hi,

For this what you have to do is that you have to create the invoice should be generated from the code by taking the inputs of newly added module records..

Suppose if your module is a fleet rental, once the renting is done, we have to give the invoice to customer, for this purpose you can add a new button in the rental record for creating invoice like we have the create invoice button in sales.

In the button action, the invoice has to be generated.

values = {}

self.env['account.invoice'].create (values)

The values is the dictionary containing the values to create the invoice, and by calling the create method of the invoice and passing values you can create invoice.

Also give account module in depends of your module.

Thanks