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The validation process has changed and now you don't need to generate API key. You just need the purchase code to validate X Theme. Please take a look at the validation guide for more information.
I checked the website and can see that you are using X Theme 4.1.1 and Cornerstone 1.0.6. For new validation process, please update X Theme and Cornerstone to latest version manually as the version of X Theme and Cornerstone that you have on the website, automatic update won't work.
You can take a look at following resources to update.
Please scroll down to Manual Update section on instructions to manually update X and Cornerstone.