Gas Manager Message: "Only growth, scale, or enterprise customers can create Mainnet policies" (for testnet)

[derwaldgeist]

I am trying to setup a gas manager policy for Polygon Amoy via the endpoint

https://manage.g.alchemy.com/api/gasManager/policy

However, I get this error message:

{
    "message": "INVALID_ARGUMENT: Only growth, scale, or enterprise customers can create Mainnet policies. Upgrade your account at: https://dashboard.alchemy.com/settings/billing."
}

which is strange because Amoy is a testnet. I also tried eth-sepolia with the same result.

Here's my payload:

{
  "policyName": "My Policy",
  "policyType": "sponsorship",
  "appId": "<myappid>",
  "rules": {
    "maxCount": "100",
    "maxCountPerSender": "2",
    "startTimeUnix": 1674228753,
    "endTimeUnix": 2147480000,
    "sponsorshipExpiryMs": 600000
  },
  "networks": ["POLYGON-AMOY"]
}

I am also wondering what this comment on the pricing page means:

Gas Sponsorship Base Limit: "Alchemy fronts the gas up to the base limit and puts the USD equivalent on your bill at the end of the month. To sponsor gas beyond the base limit you will need to buy gas credits in USD."

We have a platform where we want creators to pay the Gas Manager fees upfront via a deposit on an account associated with their own Gas Manager policy instead of us as the platform provider. Is this possible with Alchemy?

Also, what are "growth" and "scale" accounts? I can only see an upgrade option to "pay as you go".