There may be an issue with the "Thickness" value being submitted for LETTERS and FLATS.
A product has 1.25 x 0.563 x 0.25 (LxWxH) at 1oz and by itself returns fine.
But when 2x+ of that same product is submitted, I can see in the debug that the thickness used by USPS is set to the width (.563) rather than the height (.25 x 2 = .5), which is really the true thickness.
Not sure if that is USPS flipping it on its own or something the plug-in does upon submission.
But that doesn't seem right and will likely cause problems.
Is the plugin taking the shortest of width or height and submitting that as thickness?
I could swear during testing last week it the product height was used for thickness, and adding them together, i.e., 0.25 x3 = 0.75
Results for 1 product (.501 oz added for packaging via plugin) where it uses .25 for the thickness.
<pre>Array
(
[weight] => 1.501
[length] => 5
[height] => 3.5
[thickness] => 0.25
[processingCategory] => LETTERS
)
</pre>
Results for 2 products (.91 added for flats packaging in plugin), but now it is using the .563 for thickness (I think it should be .5)
<pre>Array
(
[weight] => 3.91
[length] => 11.5
[height] => 6
[thickness] => 0.563
[processingCategory] => FLATS
)
</pre>
Results for 3 products (not that thickness isn't used anymore in the results, but width of a single product is used as height now:
<pre>Array
(
[weight] => 0.244375
[length] => 1.25
[width] => 1
[height] => 0.563
[originZIPCode] => 21813
[destinationZIPCode] => 66503
[priceType] => RETAIL
[mailClasses] => Array
(
[0] => ALL
)
)
</pre>