Hi @v3madmin
You can use the field name if the value has been initialized in the database at least once. You can do it by saving the post from the backend editor or front end form. But if the value is not initialized yet, you need to use the field key so ACF knows which field you want to add since you can have different custom fields with the same name. It will prevent the confusion in the system.
But if you still think that this is a bug, you can create a new ticket from the following link so it can be passed directly to the plugin author: https://support.advancedcustomfields.com/new-ticket.
I hope this makes sense 🙂
