First, login as admin, and go in Settings.

Go in the Finances tab, and make sure Tool used for subscriptions is Stripe. Just create an account in Stripe and fill your Stripe credentials in Settings-> Finances.

Now go to “Pricing Plans”, edit/add the plan, and enter the “price_id” . One common mistake is to use plan_id instead of price_id.

So you should use the price_id from Stripe.

As you can see in the image.