Is your admin-ajax.php blocked from front end?
Can you please give me access to your website so that i can try?

Not file permission, Some website block admin access for users.
Please give me credentials here, check “Set as private reply”

i see it is working.
Can you please clear your browser cache and try again.

which user you are logged in? Please login with user details what you gave to me, then try.
Let me know.

your admin-ajax.php is blocked for non admin users by any other plugin or custom code. So non admin users can not create ajax request from front end.
You should consider unblock admin-ajax.php

When non admin user try to access your website admin area they see a error that they do not have permission to access. Which plugin show that error message?

please log in to your website as non admin user, Then try to access your website back-end. You will see a error message.
Which plugin/theme showing that message?
If you do not know then please change your theme to default theme and then try to access your back-end, If you can access then your theme is doing that. Otherwise any plugin is doing that.