setup problem

Hello,
I am trying to install the plugin, I installed the plugin but when clicking the “Appointments” (http://localhost/wordpress/wp-admin/admin.php?page=simply-schedule-appointments) I always get to an error page saying: “Oh, for fox sake, We ran into a problem: Not Found”
I traced it to some “wp-json” endpoints like:
/wp-json/ssa/v1/notices
/wp-json/ssa/v1/fetch-guides?ssasc-edition=186&ssasc-plugin-screen=395
that are returning 404 not found.

I am new to wordpress and plugins, so any help is appreciated.

Regards