Here is the reply I got from support. Apparently we need to have photos of all of the packages with weight and measurements.
I am sending this email as a follow up regarding your concern with the shipping label adjustment email you received.
As promised, I have check with one of our support team and as per what they have checked, when the shipping carrier determines that you’ve provided inaccurate information that results in an incorrect shipping label price, a shipping label price adjustment occurs. When these adjustment charges are incurred they appear on the order the label was purchased for and are charged to merchants through Shopify’s billing system.
In this order, USPS was the one who was able to sort this one out and bill you on your Shopify account. Carriers have scanners that scan the shipment’s size and weight in transit. Carriers will often round off measurements to the nearest whole inch. For example, 1.00” to 1.49” will be considered 1”, and 1.50” to 1.99” will be considered 2”. This may be the reason why you are charge of the shipping label adjustment on the said order.
No, if you wanted us to proceed with the dispute, we will be needing a photo evidence, a proof showing the weight or sizes of your shipment. Once receive, we can refer the dispute over to our designated Business Operations team.
I appreciate your time and care in this.