Hi,
The main reason for the problem is the new WordPress 5.5. At this moment we are working on a big update XStore 7.0 and it will be released soon. Meanwhile, you need to downgrade the WP version – https://techmighty.co.in/downgrade-wordpress-5-5-to-5-4-2-manually/ or update Massive Addons plugin https://www.8theme.com/documentation/xstore/plugins/plugins-update/
Regards















