Have an enum select dropdown for a type in a custom field

Currently working though a custom field plugin, and have most of what im wanting up and running now. Im running into a problem defining the options for the plugin. I want to have a type as enum so the user can select from 1 of 3 options within that dropdown. but when i set the code to below strapi does not render the component correctly.

Looking at the built in fields, the date picker field appears to have this functionality so i assume its possiable, but any help in the syntax would be great.

      options: {
        base: [
          {
            intlLabel: {
              id: getTrad(`${name}.enum-group`),
              defaultMessage: "Enum Group"
            },
            name: "options.enumSelection",
            type: "string",
            enum: [
              "a",
              "b"
            ]
          },
        ],
}

this is what i have within those settings riught now, i have swapped the type back to string for the time being and just manually typing the correct text in, but this just opens to human error so want to remove this if possiable.