admin-post-form.php

    function gaziwelfare_members_page() {
        global $wpdb;
        $table_name = $wpdb -> prefix . 'donors';

        echo "<h2>All donor list</h2>";

        $id = $_GET['mid'] ?? 0;
        $id = sanitize_key( $id );
        if ( $id ) {
            $result = $wpdb -> get_row( "select * from {$table_name} WHERE id='{$id}'" );

        }
        ?>
        <div class="form_box">
            <div class="form_box_header">
                <?php _e( 'Add member Form', 'gaziwelfare' ); ?>
            </div>
            <div class="form_box_content">
                <form action="<?php echo admin_url( 'admin-post.php' ); ?>" method="POST">
                    <?php wp_nonce_field( 'member', 'member_nonce_field' ); ?>
                    <input type="hidden" name="action" value="add_member">
                    <label for="name"><strong>Name</strong></label><br/>
                    <input type="text" name="name" id="name" value="<?php if ( $id ) {
                        echo $result -> name;
                    } ?>"><br>
                    <label for="phone"><strong>Phone</strong></label><br>
                    <input type="tel" name="phone" id="phone" value="<?php if ( $id )
                        echo $result -> phone ?>"><br>
                    <select name="status" id="status">
                        <option value="0" <?php if($id) selected( $result -> status, 0 ) ?>>Pending</option>
                        <option value="1" <?php if($id) selected( $result -> status, 1 ) ?>>Approved</option>
                    </select>
                    <?php
                        if ( $id ) {
                            echo '<input type="hidden" name="id" value="' . $id . '">';
                            submit_button( 'Update Member' );
                        } else {
                            submit_button( 'Add Member' );
                        }
                    ?>
                </form>
            </div>
        </div>

        <?php
    }

    function admin_add_member() {
        global $wpdb;
        $table_name = $wpdb -> prefix . 'donors';

        $nonce = sanitize_text_field( $_POST['member_nonce_field'] );
        if ( wp_verify_nonce( 'member_nonce_field', 'member' ) ) {
            $name   = sanitize_text_field( $_POST['name'] );
            $phone  = sanitize_text_field( $_POST['phone'] );
            $status = sanitize_text_field( $_POST['status'] );
            $id     = sanitize_text_field( $_POST['id'] );

            if ( $id ) {
                $wpdb -> update( "{$table_name}", [
                    'name'   => $name,
                    'phone'  => $phone,
                    'status' => $status
                ],
                    [ 'id' => $id ] );
                wp_redirect(admin_url('?page=gazi_wf_donor&mid=').$id);
                exit();
            }else{
                $wpdb -> insert( $table_name, [
                    'name'   => $name,
                    'phone'  => $phone,
                    'role'   => 'member',
                    'status' => $status
                ] );
                wp_redirect(admin_url('?page=gazi_wf_donor&action=created'));
                exit();
            }
        }

    }

    add_action( 'admin_post_add_member', 'admin_add_member' );