Microsoft List Form blank after configuring layout

I added some JSON to configure the body layout of a Microsoft List, and now the form shows up empty and I am no longer able to configure or edit anything (nothing happens when I press the buttons).

How can I fix this?

The only obvious error I can see with my JSON is that in the last section I had "Fields" instead of "fields".  The JSON was accepted as valid by the editor.

{
	"sections": [
		{
			"displayname": "Promo Info",
			"fields": [
				"Title",
				"BU",
				"Owner",
				"MS",
				"Folder"
			]
		},
		{
			"displayname": "Review Stages",
			"fields": [
				"Preproduction",
				"Production",
				"Review",
				"Production Update",
				"Final QC"
			]
		},
		{
			"displayname": "Web Team",
			"Fields": [
				"AEM",
				"Proof"

			]
		}

	]
}