Error "payer.payer_info.billing_address The combination of country and city is invalid"

Why did I have this error?

PayPalService. CreatePayment. payment.json={"intent":"sale","payer":{"payment_method":"paypal","payer_info":{"billing_address":{"country_code":"IT","postal_code":"20101","state":"MI"}}},"transactions":[{"amount":{"currency":"EUR","total":"21.70","details":{"subtotal":"11.64","shipping":"6.15","tax":"3.91"}},"description":"Mystore.com","invoice_number":"067ba841-4861-409b-ad1f-1dc117f74ae1","item_list":{"items":[{"name":"Item(s)","quantity":"1","price":"11.64","currency":"EUR"}],"shipping_address":{"recipient_name":" ","city":"Milano","country_code":"IT","postal_code":"20101","state":"MI"}}}],"redirect_urls":{"return_url":"https://www.mystore.it/paymentpaypalstandardpro/confirmorder","cancel_url":"https://www.mystore.it/paymentpaypalstandardpro/cancelorder"}}
2019.07.13 20:23:13:9694*******
Error. PayPalService. CreatePayment. (PayPalException).
    PayPal error: Invalid request - see details (VALIDATION_ERROR)
    payer.payer_info.billing_address The combination of country and city is invalid

Why didn't you use the city for billing address?
You use only city for shipping address.
Example

"billing_address":{"country_code":"IT","postal_code":"20101","state":"MI"}}
"shipping_address":{"recipient_name":" ","city":"Milano","country_code":"IT","postal_code":"20101","state":"MI"}

PayPal needs it.