I assume you meant the Xtreme Plus Plugin license.
Even if the Plus plugin license would not work, you could still use everything normally. The only thing you would loose is the possibility to update the plugin to a new version.
But everything else would work just as usual.
So whatever is happening with your customizer is unlikely caused by that.
For @weaver to offer suggestion, it would help if you could be more precise about the error you get, when do you get it and were and the exact text.
Also, If you have installed the Xtreme Theme Support plugin, you could still access all the theme options in the legacy Admin found in Appearance > Xtreme Admin > Main Option page. Check if that part works.