Prerequisite: this feature is available depending on your subscription plan.
Steps
At the bottom left, click Settings, then My account.
Find the Logo box and click Add.
Select your file, preferably in PNG format, then confirm.
To change your logo later, click on it: the edit form opens.
Where does your logo appear?
On letter headers.
On the PDF of the late-payment details.
On financial and operational reports (aged balance, rental situation, etc.).
On payment notices.
On rent receipts.
On sales invoices (rent invoice, etc.) and debit notes.