Shipping underpay.??

[kteach27rr]

Received two notices today that I had underpayment updates on shipping labels....

Here's the thing the weight I paid for on the shipping label was actually MORE than the weight USPS updated on the notice.

How can I be underpayment when USPS saying the package was lighter than I paid for? BTW were talking Oz. Difference not pounds.

I double checked notices to make sure it said underpayment and that the weight from USPS was reported as less than the label I created.  Hmmmmm

[worldcoinauctions]

The only thing I can think of is if you shipped ground advantage but used some priority packaging inside your package and they found it, or shipped it media rate and it wasn't eligible.

[ebooksdiva]

I agree with @worldcoinauctions.

Using packaging meant for priority for anything other than priority you will be charged. 
I noticed that you have economy shipping in some of your listings. Economy is Media mail, media mail is for recorded media and books. Not machine parts and the like. 

[nobody*s_perfect]

The problem might be the dimensions, not the weight. A few months ago, eBay introduced "cubic" rates for both Priority Mail (up to .5 cubic foot) and Ground Advantage (up to 1 cubic foot).  For those rates, even a fraction of an inch can make a difference.  For example, a package that's 8x8x8 inches ships at the rate for .3 cu ft, and 8x8x9 ships at the  .4 cu ft rate.