Hi,
We are using the official USPS address validator to check the addresses. You can check here that the address isn’t valid (according to USPS). If you change the “69” for “67”, for example, the address is valid.
Are you sure the address is valid? I’ve done a quick check on Google Maps and when you search for “69 Sheldon St” it points you to a house, but when you open Street View the address is “5 Sheldon St”.
I’m afraid you won’t be able to purchase a label for that address using our service (or any other online service). USPS simply won’t let any automated system purchase a label for what it considers to be an “invalid” destination. Maybe in this case you’ll have more luck going to the post office and talking with a human ??