You can double-check the configured settings in FileZilla and make sure that the
ssh-key is added/present.
After you install FileZilla, you need to configure it to connect to the Droplet.
Open FileZilla and then click Settings in the Edit drop-down menu.
In the Connection section, click SFTP. This is where you add your Droplet’s private SSH key. Click Add key file…, then locate your Droplet’s private SSH key on your local machine. If FileZilla prompts you to convert the file into a supported format, click Yes.
After you add the SSH key, open the File drop-down menu and click Site Manager. The site manager lets you add, remove, and manage servers and devices that you want to connect to using FileZilla.
Click New Site and enter the name of the Droplet. In the protocol field, select SFTP from the drop-down menu. Enter information for the following fields:
- Host: The IP address of your Droplet.
- Port: Enter the port you use to connect to the Droplet (port 22 is the default).
- Logon Type: Select Interactive.
- User: Enter the username you are connecting to the Droplet with (root is the default user on most Droplets).
Once you have entered your settings, click Connect. The status field in the top window displays the status of the connection.
You can check this article on How to Transfer Files to Droplets With FileZilla
and also this one How To Use Filezilla to Transfer and Manage Files Securely on your VPS
Hope that this helps!