In order to add a custom field to an accessory, you'll need to add the custom field to the category the accessory is using. That way, it will appear for all accessories using that specific category.

Let's add a custom field to the accessory below, an Apple Magic Keyboard.

Start by clicking on the category of the accessory.

Now, click on the Edit button.

Scroll down on the page until you see the Custom Fields section, and click on the Show button. This is where you can add your own custom fields that will appear for all accessories using this category.

These are the types of custom fields you can create:

You can also choose if the custom field should be a required field or not. To add options to a Dropdown List custom field, you just need to fill out the Dropdown List Content field using this format: ["Option 1", "Option 2", "Option 3", ...]

In this example, we've added two custom fields; Wireless (Checkbox) and Color (Dropdown List).

Once you've added the custom fields, scroll down and click on the Save button. Then, go back to the accessory page and click on Edit Accessory.

After scrolling down to the bottom of the page, we can see that the custom fields we added are now visible and can be filled out for the accessory!

Once we've filled out the custom fields and saved, we can see that they now appear for the accessory!

In order to remove a custom field from an accessory, you just need to go back to the Custom Fields section of the Edit Category page and make the Field Title field empty for the custom field you'd like to delete, and click Save.