How do I map enums?

I have a prop that is an enum. But no matter what I do I can't save the setting on the manage display page of my content type. I've tried making it an integer type, string type, with quotes and without quotes and nothing works. I keep getting this error even though I have one of the fixed values selected.
Max Height: Does not have a value in the enumeration ["10","12","15","20"] [JSON Schema violation of "enum"]

props:
  type: object
  properties:
    max_height:
      type: string
      title: Max Height
      description: Height in px
      enum: ['10', '12', '15', '20']
      default: '15'
      examples: []