Re: USPS RateV3 vs. RateV4
We've been using the RateV4 plugin and it sure helps since we filter by product volumes so that the FlatRate boxes are removed from the choices presented to the customer when the combination of products will no longer fit within the box. We are currently using it with 2 sites running zencart V1.3.9h. It seems to be funtioning in our V1.5 sandbox without any obvious issues.
That being said, there are is one glitch that is easily remedied and another that might not be an issue for you.
First class International: The USPS changed the terminology for in 2012. I don't remember which way but the word package changed to parcel or parcel changed to package. Make that change and the issue with International first class is corrected.
Domestic Regional C FlatRate boxes are not implemented because they were introduced in 2012. If you don't use them, then that will not be an issue.
Flat Rate Express introduced a new addition in 2012 that is not implemented.
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