Upsell was blocked due to lack of purchase permission.

Hello. I'd like to add inskill purchases to my Alexa Skill. So, my skill is hosted on a node.js server and is 100% javascript based.

I have already implemented the initiation of the purchase-sequence by responding to an incoming intent with some similar JSON like you can find below:

directives = [{
  type: "Connections.SendRequest",
  name: "Buy",
  payload: {
    InSkillProduct: {
      productId: "amzn1.adg.product.$productid$"
    },
  },
  token: "{}"
}]

This purchase logic works great, just as it should but I got some problems implementing a Upsell-logic sending back this JSON:

directives = [{
  type: "Connections.SendRequest",
  name: "Upsell",
  payload: {
    InSkillProduct: {
      productId: "amzn1.adg.product.$productid$"
    },
    upsellMessage: "$upsellmessage$"
  },
  token: "{}"
}]

So every single time sending back the payload above I get the error message "not a valid request".

I found out that the Alexa response says "Upsell was blocked due to lack of purchase permission." - so to my question: How can I fix this issue and whats the reason for this at all?

"request": {
  ...
  "name": "Upsell",
  "payload": {
    "purchaseResult": "ERROR",
    "productId": "amzn1.adg.product.$productid$",
    "message": "Upsell was blocked due to lack of purchase permission."
  }
}