Contact Form 7 - Success Page Redirects version 1.2.0 plugin fix (fixes conflict with Flamingo add-on and also makes it work with & without AJAX enabled on the form) as mentioned on https://wordpress.org/support/topic/compatibility-issue-with-flamingo-official-plugin-for-storing-cf7-submissions/

cf7-success-page-redirects.php

<?php
/**
 * Plugin Name: Contact Form 7 - Success Page Redirects
 * Description: An add-on for Contact Form 7 that provides a straightforward method to redirect visitors to success pages or thank you pages.
 * Version: 1.2.0
 * Author: Ryan Nevius
 * Author URI: http://www.ryannevius.com
 * License: GPLv3
 */

/**
 * Verify CF7 dependencies.
 */
function cf7_success_page_admin_notice() {
    // Verify that CF7 is active and updated to the required version (currently 3.9.0)
    if ( is_plugin_active('contact-form-7/wp-contact-form-7.php') ) {
        $wpcf7_path = plugin_dir_path( dirname(__FILE__) ) . 'contact-form-7/wp-contact-form-7.php';
        $wpcf7_plugin_data = get_plugin_data( $wpcf7_path, false, false);
        $wpcf7_version = (int)preg_replace('/[.]/', '', $wpcf7_plugin_data['Version']);
        // CF7 drops the ending ".0" for new major releases (e.g. Version 4.0 instead of 4.0.0...which would make the above version "40")
        // We need to make sure this value has a digit in the 100s place.
        if ( $wpcf7_version < 100 ) {
            $wpcf7_version = $wpcf7_version * 10;
        }
        // If CF7 version is < 3.9.0
        if ( $wpcf7_version < 390 ) {
            echo '<div class="error"><p><strong>Warning: </strong>Contact Form 7 - Success Page Redirects requires that you have the latest version of Contact Form 7 installed. Please upgrade now.</p></div>';
        }
    }
    // If it's not installed and activated, throw an error
    else {
        echo '<div class="error"><p>Contact Form 7 is not activated. The Contact Form 7 Plugin must be installed and activated before you can use Success Page Redirects.</p></div>';
    }
}
add_action( 'admin_notices', 'cf7_success_page_admin_notice' );


/**
 * Adds a box to the main column on the form edit page.
 *
 * CF7 < 4.2
 */
function cf7_success_page_add_meta_boxes() {
    add_meta_box( 'cf7-redirect-settings', 'Success Page Redirect', 'cf7_success_page_metaboxes', '', 'form', 'low');
}
add_action( 'wpcf7_add_meta_boxes', 'cf7_success_page_add_meta_boxes' );


/**
 * Adds a tab to the editor on the form edit page.
 *
 * CF7 >= 4.2
 */
function cf7_success_add_page_panels($panels) {
    $panels['redirect-panel'] = array( 'title' => 'Redirect Settings', 'callback' => 'cf7_success_page_panel_meta' );
    return $panels;
}
add_action( 'wpcf7_editor_panels', 'cf7_success_add_page_panels' );


// Create the meta boxes (CF7 < 4.2)
function cf7_success_page_metaboxes( $post ) {
    wp_nonce_field( 'cf7_success_page_metaboxes', 'cf7_success_page_metaboxes_nonce' );
    $cf7_success_page = get_post_meta( $post->id(), '_cf7_success_page_key', true );

    // The meta box content
    $dropdown_options = array (
            'echo' => 0,
            'name' => 'cf7-redirect-page-id',
            'show_option_none' => '--',
            'option_none_value' => '0',
            'selected' => $cf7_success_page
        );

    echo '<fieldset>
            <legend>Select a page to redirect to on successful form submission.</legend>' .
            wp_dropdown_pages( $dropdown_options ) .
         '</fieldset>';
}
// Create the panel inputs (CF7 >= 4.2)
function cf7_success_page_panel_meta( $post ) {
    wp_nonce_field( 'cf7_success_page_metaboxes', 'cf7_success_page_metaboxes_nonce' );
    $cf7_success_page = get_post_meta( $post->id(), '_cf7_success_page_key', true );

    // The meta box content
    $dropdown_options = array (
            'echo' => 0,
            'name' => 'cf7-redirect-page-id',
            'show_option_none' => '--',
            'option_none_value' => '0',
            'selected' => $cf7_success_page
        );

    echo '<h3>Redirect Settings</h3>
          <fieldset>
            <legend>Select a page to redirect to on successful form submission.</legend>' .
            wp_dropdown_pages( $dropdown_options ) .
         '</fieldset>';
}

// Store Success Page Info
function cf7_success_page_save_contact_form( $contact_form ) {
    $contact_form_id = $contact_form->id();

    if ( !isset( $_POST ) || empty( $_POST ) || !isset( $_POST['cf7-redirect-page-id'] ) ) {
        return;
    }
    else {
        // Verify that the nonce is valid.
        if ( ! wp_verify_nonce( $_POST['cf7_success_page_metaboxes_nonce'], 'cf7_success_page_metaboxes' ) ) {
            return;
        }
        // Update the stored value
        update_post_meta( $contact_form_id, '_cf7_success_page_key', $_POST['cf7-redirect-page-id'] );
    }
}
add_action( 'wpcf7_after_save', 'cf7_success_page_save_contact_form' );


/**
 * Copy Redirect page key and assign it to duplicate form
 */
function cf7_success_page_after_form_create( $contact_form ){
    $contact_form_id = $contact_form->id();

    // Get the old form ID
    if ( !empty( $_REQUEST['post'] ) && !empty( $_REQUEST['_wpnonce'] ) ) {
        $old_form_id = get_post_meta( $_REQUEST['post'], '_cf7_success_page_key', true );
    }
    // Update the duplicated form
    update_post_meta( $contact_form_id, '_cf7_success_page_key', $old_form_id );
}
add_action( 'wpcf7_after_create', 'cf7_success_page_after_form_create' );


/**
 * Redirect the user after the submission is made & was confirmed to be successful
 */
function cf7_success_page_form_submitted_ajax( $items, $result ) {

	// Set array of acceptible statuses/cases
	$cases = (array) apply_filters( 'wpcf7_flamingo_submit_if',
		array( 'mail_sent' ) );

	// Reject the submission if it wasn't a valid status/case
	if ( empty( $result['status'] )
	|| ! in_array( $result['status'], $cases ) ) {
		return $items;
	}

	// Otherwise, continue forward as it was a successful form submission
	$contactform = WPCF7_ContactForm::get_current();
	$contact_form_id = $contactform->id();

	// Send user to a success page, if there is one
	$success_page = get_post_meta( $contact_form_id, '_cf7_success_page_key', true );

	if ( ! isset( $items['onSentOk'] ) ) {
		$items['onSentOk'] = array();
	}

	if ( ! empty( $success_page ) ) {
		$items['onSentOk'][] = sprintf(
			'window.location = "%s";',
			get_permalink( $success_page )
		);
	}

	return $items;

}
function cf7_success_page_form_submitted_noajax( $contactform, $result ) {

	// AJAX is enabled; use JavaScript to perform the redirect instead
	if ( isset( $_POST['_wpcf7_is_ajax_call'] ) || ! isset( $result['status'] ) ) {
		return;
	}

	// Set array of acceptible statuses/cases
	$cases = (array) apply_filters( 'wpcf7_flamingo_submit_if',
		array( 'mail_sent' ) );

	// Reject the submission if it wasn't a valid status/case
	if ( empty( $result['status'] )
	|| ! in_array( $result['status'], $cases ) ) {
		return;
	}

	// Otherwise, continue forward as it was a successful form submission
    $contact_form_id = $contactform->id();

    // Send user to a success page, if there is one
    $success_page = get_post_meta( $contact_form_id, '_cf7_success_page_key', true );
    if ( !empty($success_page) ) {
        wp_redirect( get_permalink( $success_page ) );
        die();
    }
}
add_filter( 'wpcf7_ajax_json_echo', 'cf7_success_page_form_submitted_ajax', 10, 2 ); // AJAX is enabled
add_action( 'wpcf7_submit', 'cf7_success_page_form_submitted_noajax', 900, 2 ); // AJAX is disabled (use really late priority to ensure all other submission actions are completed first as this will inturrupt actions)