title: Adding a Plan to an existing Product using Stripe API
body: <p>I'm currently building a platform using MERN, and have stripe API connected in the backend. </p>
  
  <p>Currently, I can retrieve all products &amp; plans, and can create a plan. But every time I create a plan, it creates a new product for said plan. And I want the plan to be added to an existing product.</p>
  
  <p>Following Stripe's API docs, this is what I currently have:</p>
  
  <pre><code>    stripe.plans.create({
        amount: amount,
        interval: "month",
        product: {
          name: fields.productName,
          id: fields.productID
        },
        currency: "eur",
      }, function(err, plan) {
      }
  </code></pre>
  
  <p>The product object contains the name and id from an existing product, but I get the following error:</p>
  
  <pre><code>message: "Product already exists."
  </code></pre>
  
  <p>Since I can do this via the Stripe dashboard, I presume it's definitely possible using API, but I can't seem to figure out what I'm missing.</p>
  
  <p>Any suggestions would be greatly appreciated</p>