How do fields[whatever] work?

I can't find any documentation or examples on this, I'm sorry if this is a dumb question.

For some reason, this call doesn't give me any of the fields[inAppPurchasePricePoints] fields I ask for:

https://api.appstoreconnect.apple.com/v1/inAppPurchasePriceSchedules/{iap_id}/manualPrices?include=inAppPurchasePricePoint&fields[inAppPurchasePricePoints]=customerPrice

This is the response I'm getting:

{
	'type': 'inAppPurchasePrices',
	'id': 'super_long_id',
	'attributes': {
		'startDate': None,
		'endDate': '2023-07-12',
		'manual': True
	},
	'relationships': {
		'inAppPurchasePricePoint': {
			'data': {
				'type': 'inAppPurchasePricePoints',
				'id': 'long_id'
			}
		}
	},
	'links': {
		'self': 'https://api.appstoreconnect.apple.com/v1/inAppPurchasePrices/super_long_id'
	}
}

Why doesn't the response include the customerPrice I'm asking for? What am I missing here?

Thank you for your patience and support!