A 403 Forbidden error message while editing your form may be the result of your hosting provider using mod_security. LiteSpeed web server, by default, has mod_security enabled.
This is not a problem with WS Form and the same issue may affect other WordPress plugins or features you are using, including simple tasks such as uploading images.
It is caused by mod_security incorrectly mistaking API requests made by WS Form as potential threats. The server will typically return a 403 forbidden error.
To stop this from happening, you can disable mod_security by adding the following code to your .htaccess file when editing forms in WS Form.
<IfModule mod_security.c> SecFilterEngine Off SecFilterScanPOST Off </IfModule>
More information on Stack Overflow. For further assistance, please contact your hosting provider.