Hello, Enderkadir,
Thank you for getting in touch with us.
You have a lot of 3rd party plugins installed on your site, one of them can be the reason for the problem with import.
Before running the demo content import, please disable 3rd party plugins first. Here you can find a list of required plugins – https://www.8theme.com/documentation/xstore/plugins/included-plugins/ , then go to XStore > Import demos.
Also, we are facing a 503 error. 503 Service Unavailable – this server error response code indicates that the server is not ready to handle the request. Common causes are a server that is down for maintenance or that is overloaded. Please contact your hosting provider and ask for assistance from their side.
This https://prnt.sc/a_CVlAm8_Ht5 also should be fixed from the hosting provider side.
Kind Regards,
8theme team