Thanks for the reply.
Please do the next.
1/ Check the situation on Checkout when the default WooCommerce theme – Storefront is activated.
Let us know the result.
2/ Try to disable all the third-party plugins (including cache plugins), that do not come bundled with XStore https://xstore.helpscoutdocs.com/article/36-included-plugins , clear the cache of the browser, and check then. Maybe one of the additional plugins is the reason for the problem (another plugin may conflict with our theme and cause js error which breaks the work of the WooCommerce Payments plugin).
Let us know the result.
3/ Please provide temporary wp-admin and FTP access.
Create an account via Dashboard (Users > Add new) with administrator role http://prntscr.com/s3rc9m > provide us with username and password via the Private Content area http://prntscr.com/s5mao7 You can use any email for it.
If you do not know how to create FTP contact with your hosting provider, they will help you.
Regards