Experiments Api - "Create" endpoint returns 500

Hey, when I try to create an experiment using the API I just get Error code 500 "Internal Server Error" as response. This happens I call the API from my retool application, but also when using curl from my local machine.

My networking tab shows that I send this request:

"request": {
    "url": "https://experiment.amplitude.com/api/1/experiments",
    "method": "POST",
    "body": "{\"key\":\"test-api-call\",\"name\":\"Test\",\"description\":\"Try to create an experiment using the API\",\"projectId\":******}",
    "headers": {
      "Content-Type": "application/json",
      "User-Agent": "Retool/2.0 (+https://docs.tryretool.com/docs/apis)",
      "Accept": "application/json",
      "Authorization": "---sanitized---",
      "ot-baggage-requestId": "undefined",
      "x-datadog-trace-id": "5857767016106236026",
      "x-datadog-parent-id": "5648445407639375651",
      "x-datadog-sampling-priority": "0",
      "x-datadog-tags": "_dd.p.dm=-1",
      "traceparent": "00-0000000000000000514af810bc03187a-4e634f2be7880f23-00",
      "tracestate": "dd=t.dm:-1;s:0",
      "X-Retool-Forwarded-For": "85.243.168.150"
    }
  },

All other experiments API endpoints (that I need) are working fine for me, and I double checked that my request has the the correct URL and contains all required parameters (projectId and key).
I also tried to create new API keys, but all have the same issue.

Any help is appreciated.