If the payment module has already been installed, you must delete the payment_payzen folder from the addons directory.
The addons directory can be found via:
- /server/odoo/addons/ for Windows servers.
- /var/lib/odoo/addons/[VERSION]/ for Linux servers.
If there are no addons in any of these paths, check the addon_path line in the odoo.conf file. The path indicates the location of addons.