Additional shipping cost need to be applied.

[macbase]

Found that cost of shipping more than indicated on eBay purchased label due to extra weight. How can the additional cost be applied to a pre purchased label.

[klhmdg]

you can not add to an already purchased label.

You will need to cancel the 1st label and buy a new correct label.

[fern*wood]

Are you saying your information on the label was wrong and you didn't correct it before printing/paying for the label?  If it was USPS and hasn't shipped yet, I would void the label and print correctly.

[macbase]

How do you cancel / Void a label?

[macbase]

How do you void/cancel a shipping label?

[kensgiftshop]

You have 5 days to void the shipping label.
Go to your shipping labels and click Void in the menu next to the label.
It'll take 3 to 4 weeks to receive the refund.
https://www.ebay.com/lbr/labels-history/seller-hub

[toysaver]

I've been able to add to a printed label from home at the USPS counter.  They'll re-stamp the additional postage.  

[macbase]

Yes, the information regarding was incorrect.  The weight in the box was found was found, after printing the label, to be a few pounds more.

[mtgraves7984]

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@macbase wrote:

How do you cancel / Void a label?

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@macbase 

Find the order (Seller Hub/Orders/Paid and shipped) and use the drop-down menu to the left to 'Void label'. Next... use the same drop-down menu to 'Purchase another label'.