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Email:         [email* your-email]
Confirm email: [email* your-email-confirm]

** ADD THIS IN FUNCTION.PHP
add_filter( 'wpcf7_validate_email*', 'custom_email_confirmation_validation_filter', 20, 2 );
 
function custom_email_confirmation_validation_filter( $result, $tag ) {
    if ( 'your-email-confirm' == $tag->name ) {
        $your_email = isset( $_POST['your-email'] ) ? trim( $_POST['your-email'] ) : '';
        $your_email_confirm = isset( $_POST['your-email-confirm'] ) ? trim( $_POST['your-email-confirm'] ) : '';
 
        if ( $your_email != $your_email_confirm ) {
            $result->invalidate( $tag, "正しいメールアドレスを入力して下さい" );
        }
    }
 
    return $result;
}