Thanks for writing in!
I checked the website and can see that you are not using X Theme and looking at the screenshot it seems that you are trying to upload the theme.
Just wanted to confirm, after downloading the package from Themeforest (if you downloaded X Theme fro Themeforest), have you extracted the zip file. I have seen that most of the time customers downloading complete theme package and trying to upload that whole file. If you have selected All files & documentation option then please extract the file and upload the installable x.zip file or you can select Installable WordPress file only option that you can upload.
In case you face any issues, please share website login details in secure note for us to take a closer look at the setup.