Why is my custom field not working?

Can't type the field name.

When you go to use a custom field in a message, you must select it from the fields list. Typing the name of the field doesn't work.

Checking it in the preview.

When you are previewing your bot in the bot builder, it will show the custom field name because there is no stored data. This is not what the bot will look like on your live site. If you wish to preview your bot with real data, use the Preview As feature.