WP check_ajax_referer() is not working

One is When I use the shortcode of the form in the page or post,
showing the form in the WP backend 5.2.3 version.

That happens because your shortcode is echoing the output. A shortcode should always return the output, but if you need to echo it, then you should use output buffering:

public function ajaxrf_shortcode(){
    // Turn on output buffering.
    ob_start();

    self::AjaxdataProcess();
    self::ajax_reservation_form(); // echo the form

    // Turn off output buffering and then return the output echoed via the above functions.
    return ob_get_clean();
}

Another one is when I check the nonce field using this function
check_ajax_referer(). The form does not appear in the view page.
Only showing -1 in the view page.

First off, why are you calling AjaxdataProcess() in the shortcode function (ajaxrf_shortcode())? Is it because you are allowing non-AJAX form submissions?

But that “-1” could happen if the (AJAX) request verification failed (e.g. due a missing or an expired nonce) and by default, check_ajax_referer() will call either wp_die() if doing an AJAX request or die() otherwise.

And to prevent WordPress/PHP execution from being halted upon failure of the request verification, set the third parameter to false when you call check_ajax_referer():

check_ajax_referer( 'rsf_nonce_action', 'snonce', false )

If you want to allow non-AJAX form submissions…

1. Make sure the relevant form fields are assigned the proper name; e.g.:

   <input type="text" class="form-control" id="RFname" name="RFname">
   <input type="email" class="form-control" id="RFemail" name="RFemail">
   

2. You should also set the form’s method to post (because AjaxdataProcess() is using $_POST):

   <form action="<?php the_permalink(); ?>" id="arform" method="post">
   

3. Although your form does include the proper nonce, WordPress/PHP doesn’t recognize it because you’re not using the proper name — you used snonce with check_ajax_referer() (and in your JS script), but in the form, the name is rsf_nonce_field:

   • In ajax_reservation_form() — the value of the second parameter for wp_nonce_field() should match the value of the second parameter for check_ajax_referer() (and in fact, same goes to the first parameter..):

     <?php wp_nonce_field( 'rsf_nonce_action', 'rsf_nonce_field');?>
     

   So that rsf_nonce_field should be changed to snonce.