I had the same problem. I created a “Zendesk Chat” account within the “Zendesk Support’s Dashboard”, installed the “Zendesk Chat Plugin” for WordPress on my server, and then I tried to link the “Zendesk Chat” to my WordPress site. Keep getting an ivalid credential error.
After some troubleshooting, I am inferring the following: The “Zendesk Chat” account created by the “Zendesk Support’s Dashboard” uses some internal credentials, when the accounts are linked, but there are not disclosed to the “Zendesk Support’s Admin.
To test if this was the case, I created a new “Zendesk Chat” account using the URL https://www.zopim.com (this is the old URL for “Zendesk Chat”) with a new set of credentials. I used those new credentials to link this account to the “Zendesk Chat” Plugin on WordPress. It worked well.
I contacted Zendesk Help to ask them how to link the account I created in https://www.zopim.com with my “Zendesk Support” account. However, I have not received a response from Zendesk as of today.
Hope they provide information to either get the internal “login credentials” from the Zopim account liked to the “Zendesk Support” account, or a way to remove the “Zendesk Chat” from Zendesk Support and link the one I created in https://www.zopim.com.
I will keep you posted when I get a response.