Cannot install Trial Helpdesk App

Trying to install the trial version while I await my full license I purchased but get the following error during the wizard installation:

17:54:39: Registering HelpDesk application...
17:54:44: Call failed with status code 500 (Internal Server Error): POST https://helpdesk-installer.plumsail.com/2.1.19/New

Any help greatly appreciated.

Hello! Do you have a HelpDesk site installed? If so, please open it, then navigate to Settings > About and renew the client secret using the global admin credentials. The legacy authentication should be allowed in your tenant and the MFA should be disabled - otherwise, use an app password. Let me know whether it worked.

Evgeniy, I have no helpdesk installed at all. This was a clean fresh install to our tenancy.

I sent you instructions to renew client secret through private message.

Renewing the client secret helped.