Viper FTP User Guide
Viper FTP manages files located in many different folders on your Mac disk. Some folders (eg. Trash) will not be accessible until you grant Full Disk Access for Viper FTP.
To grant the Full Disk Access, open System Preferences, click Security & Privacy icon and select Privacy tab:
Then click the lock icon at the bottom to make changes. On the list select Viper FTP checkbox:
If Viper FTP is not on the list, click "plus" button to add it: