1. Is your site a multisite? If so, AND if the plugin is network-activated, then you will find the wallets sub-menu under the network admin menu, not the site-level menu.
2. If the above is not the case, then I’m not sure why this would happen. Could you try disabling other plugins, or possibly switch to another theme to see if that helps?
3. Do you see any errors in your WordPress debug log? You would first have to enable logging: https://codex.wordpress.org/Debugging_in_WordPress
I could also login to your site to have a look if you like.
kind regards