I'm trying to store an object to Firestore. My object contains an array:

{
  returnMode: false,
  id: "SE-74c5219a-acfe-4185-9e33-f78b10ac3f1e",
  prices: [
    {
      price: {
        twoHours: 0,
        firstHour: 0,
        id: "zero",
        unlock: 0,
        final: 0,
      },
      permission: { id: "GENERAL" },
    },
    {
      price: {
        twoHours: 150,
        unlock: 100,
        id: "oebb_low",
        firstHour: 50,
        final: 50,
      },
      permission: { id: "OEBB" },
    },
  ],
}

If this object is hard-coded into the Cloud Function it lets me save it to Firestore without failing. If I replace the array of the above object with a variable like so it still works:

const array = [
    {
      price: {
        twoHours: 0,
        firstHour: 0,
        id: "zero",
        unlock: 0,
        final: 0,
      },
      permission: { id: "GENERAL" },
    },
    {
      price: {
        twoHours: 150,
        unlock: 100,
        id: "oebb_low",
        firstHour: 50,
        final: 50,
      },
      permission: { id: "OEBB" },
    },
  ];
{
  returnMode: false,
  id: "SE-74c5219a-acfe-4185-9e33-f78b10ac3f1e",
  prices: array,
}

However, when the above array is not hard-coded into the Cloud Function but created by my program, it fails. This is the code that generates the array:

const bikeBoxPriceArray = [];

for (let i = 0; i < bikeBoxPermissionArray.length; i += 1) {
  const doc = bikeBoxPermissionArray[i];
  // I cut out the stuff that is not important

  const bikeBoxPriceArrayElement = {
    permission: {
      id: doc.id,
      name: doc.name,
    },
    price: {
      id: priceId,
      unlock: priceUnlock,
      firstHour: priceFirstHour,
      twoHours: priceTwoHours,
      final: priceFinal,
    },
  };

  bikeBoxPriceArray.push(bikeBoxPriceArrayElement);
}

I verified with bikeBoxPriceArray instanceof Array that it is indeed an array. What am I doing wrong? I tried out many many things but I just cannot figure it out. Why is it working when hard-coded but not with the variable?

The code is inside of a Firebase Transaction and there is no error message, it just tells me the location of the error.