The topic has been answered by mail.

I am Leo. We have purchased the plugin called - (wpForo – Topic Prefix & Tag Manager) for our fourm website two days ago. 

But Yesterday, we decided to change the domain name (same wordpress site, just change the domain name), after we changed the domain name from old domain name (augameguild.com) to the new domain name (coolrabbit.com.au).

We hired a developer to do this for us. After we changed the domain name, we found that all the features of WordPress go well, but only the Tage Manager Plugin couldn't work.

The developer guess that we have used the license key of the plugin to bind to the old domain name, but the new domain name could not be accepted due to there is no license key. 

Because of the old domain didn't work now (we changed the domain name for the same wordpress site), we could not disconnect the license under the old domain name. And we did not done the job (disconnect the license) before we changed the domain. 

I have opened a topic in wpForo Community, the admin said that I should go here to ask a solution due to this is a license problem. 

Therefore, how we could fix this issue?

Thank you so much for your help, which is vital to us.

Yours Sincerely,
Leo