White screen on activation and "used" license

Hi everyone, today I bought the theme of “Ametex” and at the moment of activating it with the license that I downloaded from the website for a millisecond this appears:

And then it goes blank (the first image is thanks to a quick capture)

I don’t understand what happens, I have never used that license and it is the first time I do this. Please help me

It looks like there might be an error preventing that page from working properly. Please contact the author of the theme for support, as this is something they will need to look into and fix for you.

Here’s their support information – https://themeforest.net/item/ametex-digital-marketing-and-seo-wordpress-themes/23986132/support