While saving the settings using Print Invoice, Packing Slip, Delivery Note & Label Plugin for WooCommerce plugin, you may have come across an issue ‘Unable to save the settings‘.
The cause of this issue is usually due to the installed Firewall on your website. WordFence and Sucuri are identified as common firewalls causing issues. The firewall may be blocking the action used for saving the plugin settings.
The common workaround that we would suggest would be to whitelist the action that is blocking the settings from saving. Note that the user with admin provisions will only have access to whitelist the action.
If your issue still persists, then you may require technical support to get it resolved.