My Server IP has changed and I got License Invalid error message
Whenever the Server IP, WHMCS Domain or WHMCS Installation path has changed, you need to re-issue your licences. You do exactly the same for your WHMCS License
Login into our client area and click the “My Products / Services” link from the client menu. Click the Button for the license Details and from the products details page click the tab "Management actions" > "Reissue Licence".