Save data of select list after clicking save

You have the add_action that’s supposed to hook your prfx_meta_save function inside the function itself, so it never gets hooked or called. You need to move the add_action outside the function.

This will never work:

function prfx_meta_save( $post_id ) {
    add_action( 'save_post', 'prfx_meta_save' );
}

Move it outside the function:

function prfx_meta_save( $post_id ) {
    // your save code
}
add_action( 'save_post', 'prfx_meta_save' );