If you're not seeing that your box content information has successfully been accepted in Seller Central, you may need to resend the information. To do so, follow the follow steps!
1. Click the three horizontal lines next to your shipment and choose 'Box Content Information'.
2. On the Box Contents page, click 'Transmit Updated Boxes'.
3. Wait for the green success message on the right-hand side of the page.
You should see that your box content information has transferred over to Seller Central at this point.
If this isn't the case, try refreshing the box content option click the three horizontal lines next to your shipment and choose 'Refresh Box Option' before checking Seller Central once more.