I have problem with this plugin. When I try change text

Hello,
I have problem with this plugin. When I try change text on email tab If I click "save changes" I get page with this error: "Oops! That page can’t be found."
With the link: ../wp-admin/network/admin.php?page=psts-settings&tab=email
I also enable debug mode but not get any error file and disable others plugins and the problem continue.

Can you help me please?
Thank you
Best Regards