If you want to redirect users to a thank you page or payment page after submission of a contact form7. Follow the below instructions.
Access the theme header.php via FTP or via Appearance > Theme Editor
Paste the below code just above <?php wp_head(); ?>
<script>
document.addEventListener( 'wpcf7mailsent', function( event ) {
location = 'http://example.com/';
}, false );
</script>
Replace the example.com with the actual website page URL.