When it comes to shipping, getting customs clearance can get be a headache. FedEx advises that you need to be as accurate as possible.
Everything that you write make sure it is legible and written in the correct spots. Mistakes, or inaccuracies, make it appear that the papers are forged. Be honest, upfront, and most of all, just do what they tell you to do. If they want you to open a container, do it with a smile.

Source: https://www.entrepreneurshipsecret.com/procedure-for-customs-clearance/