When a client accepts a taks, you can create an invoice for it. Depending on the arrangement with your client, there are two options.
1. Invoicing as soon as the client accepts the task
As soon as a submitted task gets checked and approved (status “Approved”), you can submit an invoice.
2. Monthly invoicing
You submit an invoice at the beginning of the month for all the completed tasks from the previous month. 
Knowing when you can submit an invoice
You will get notified right away in your Lano account when a client approves an assignment. 
In your dashboard you can see all the tasks that are ready to be invoiced.
Left column: tasks that can be invoiced right away.
Right column: tasks that get invoiced on a monthly basis.
Further articles
How You Can Automatically Generate an Invoice