Saving data to WooCommerce session

I’m attempting to save a simple text input to the WooCommerce session. The session is created when a user adds something to their cart.

Here’s the code I’m using to set the data

if( !is_admin( ) ) {
    // User input
    if( ! empty( $_POST['create_new_group'] ) ) {
        $group_input_value =  $_POST['create_new_group']; 

        // Set session and save data
        WC()->session->set( 'group_order_data', $group_input_value );

        wp_redirect( 'http://localhost:28/site.dev/checkout' );
        exit();
    }
}

It doesn’t set the data. Is this process correct or am I missing the point with setting sessions?