UPS/Parcel Pro requires a valid phone number from the “shipping address” to be able to print labels and to insure your orders.
1) If you want to require your customer’s phone number in your checkout, please go to Admin > Settings (bottom left icon) > Checkout and set Shipping address phone number as Required and click on Save.
2) If you do not want to require your customer’s phone number in your checkout, make sure the phone number of your store is entered correctly, because it will be used in case UPS/Parcel Pro needs to make any contact. Please go to Admin > Settings (bottom left icon) > Locations, inform the correct format number with at least 10 numeric characters and click on Save. If your client provides a non-valid phone number, your store phone number will be used instead.