Although we use only the day and month part of the Birthday for compatibility reasons the API expects a DateTime as the Birthday date.
This field is expected to have the ISO 8601 format such as 2023-02-03T14:11:10Z.
Note the trailing Z in the previous example: it means the date is in UTC format. This is important to make sure the date is correct.
Once set, the birthday date cannot be changed. If you try so the API returns an 400 error with 60 as ErrorCode property
Use API Basic Auth Keys