To issue a first partial rent, that is a rent that does not relate to a full month, you have multiple options:

• you can specify it in the Tenancy creation form. If your tenancy starts at a date other than the 1st of the month, the site will propose you the First invoice section (in the Receipts tab).
• If a rent has already been generated in the Finance section, you can edit it by changing the dates and the amounts.
• You can also add a revenue of type Rent manually in the Finance section.