The cool thing is with this issue you can run through some simple process of elimination tricks to sort out what exactly is causing the issue. With whmcs addon the more plugins you start to add in the more issues you should naturally expect. So lets cover how you will figure out if it is our plugin that is causing your current issues…

First revert back to the addon you get with whmcs , next deactivate legal app. Are you still having the issue? If so continue to deactivate your plugins 1 at a time with a refresh after each until the error or issue goes away. Now that will tell what plugin is causing the issue (keep it mind it could be the theme but that is eliminated once we revert back to stock theme), try to re-activate our plugin again. If it is working correctly and NOT “breaking” your website or causing errors then you are good to go and you should message the plugin developers to the plugin you had deactivated to fix the error/problem. They will be able to troubleshoot you further.
As a last test, reactivate the theme you had up just to make sure and see.