When writing an address with an apartment number, you should include the apartment number on Address Line 2, as shown below:
9807 Beechwood Street, Apartment 4B, Brooklyn, NY, 11219
Address Line 1: 9807 Beechwood Street
Address Line 2: Apartment 4B
City: Brooklyn
State: N.Y.
Zip Code: 11219
In this example, "Apartment 4B" is the apartment number and is included on Address Line 2. It's important to note that the format may vary depending on your country or region, so it's always a good idea to check local conventions to ensure you use the correct format.
Also, when writing an address with an apartment number, include the recipient's name, street name, city, state, and zip code, to ensure the mail is delivered to the correct address.