Don’t mix the test mode and live mode. Specially when you have subscriptions since Stripe doesn’t allow the subscription plans to be interchangeable between live mode and test mode. Mixing them up will cause too much hassle.
Once you have done a test transaction with one product and it works, it means all your API and connection setup is correct and the plugin is ready go. ALL the products you create will work fine in terms of the transaction.
Since you have live subscriptions, you need to set the settings to “Live Mode”, otherwise it won’t work.