Generate-user-token returns empty token string

I’ve followed the guide for getting a user-scoped token for the Data API: As a User - Bubble Docs

Screenshots of the setup:

The endpoint is callable at /api/1.1/wf/generate-api-token/. It worked for the first few calls but now seems to be returning an empty token string when I try generating a token again. Sample response:

  "status": "success",
  "response": {
    "token": "",
    "user_id": "<USER_ID>",
    "expires": 31536000

This occurs on live and version-test. Any idea why this is happening and how I can get another token?