Attach ACF to post category

[gavinb80]

Hi,

I am looking to add an image url to post categories which I can then pull via the Rest API.

I've created a new custom field, and if I run the API https://somewebsite.co.uk/wp-json/wp/v2/categories

I can see the ACF:

    "taxonomy": "category",
    "parent": 0,
    "meta": [],
    "acf": {
        "image-url": null,
    },
    "_links": {

But I cannot figure out how I can actually assign a value to the image-url custom field for a category.