Error 403 when saving the credentials form

This usually happens when your environment is running Mod_Security. Older rule sets trigger a false positive when WSC tries to save the initial tables to the database. To confirm this is the case you can visit the credentials form and you won't see any fields that can be filled out by end users. There are a couple of options to resolve this.

Disable Mod_Security (Temporarily) 

In cPanel you can disable Mod_Security on a per-domain basis. Navigate to the cPanel UI and search Mod_Security. Slide the slider to off and then try to attempt to save the credentials form again. This time if the form saves and you can see the WSC form fields when visiting the credentials form you know Mod_Security was the issue.

Disable Mod_Security Rule

If you have cPanel and access to WHM you can navigate to the Mod_Security section to see which rule is being triggered. This rule can then be whitelisted and ModSec enabled again. 

Update RuleSet

The latest ruleset can be installed which should resolve this issue. The latest ruleset may not be shipped with control panels like cPanel and updating ModSec rules is beyond the scope of our support. cPanel, Plesk and DirectAdmin provide support for features contained in their respective control panels.