Important if you are using USPS real-time rates this issue affects you please read below:
As of Sunday April 1st 9:15am PST, all customers using USPS real-time rates are not receiving USPS shipping rates. Please note that we are receiving the following error:
USPS:API Disabled: Rate. This API has been retired. Please use RateV4.
If you are using ONLY USPS rates and you do not have backup rates or any other type of real-time shipping enabled please do so immediately. Having a backup calculated or other real-time rate will ensure that your customers can continue to checkout during this error. If you do not have either of these and rely solely on USPS real-time rates, your customers will be unable to checkout until this issue is resolved.
Note: It is always a good idea to have backup real-time rates enabled otherwise if the shipper is unreachable for any reason or has temporary downtime etc we will still be able to present shipping rates to your customers vs an error from the shipper. There is a checkbox on the shipping method screen to make a rate a backup only rate, this means it should be displayed only when no real-time rates can be retrieved.
Unfortunately we were unaware of this change that USPS was making and it appears many others were as well as I am reading this all over the web including at third party shipping tools that used this API. We will be correcting this issue as soon as possible but this may take several days to get resolved as it will require new programming, testing etc. To ensure that your store continues operating smoothly in the meantime please follow the instructions above on either having another real-time provider enabled or using a backup calculated rate. Ie UPS, FedEx etc are are all working this issue affects ONLY USPS.
Who Does This Affect?
Anyone using USPS real-time rates with their store
What Will My Customers See?
If you have any other rates to display, ie other realtime rates or backup rates your customers will see those instead and will just not see USPS rates, they will proceed through checkout as normal. If you have only USPS realtime rates your customers will see an order and be unable to continue.
How Long Will This Take To Resolve?
Unfortunately we expect a minimum of 2 days but this will be our top priority. Until we can speak to USPS on Monday we have no further information.
How Can I Make Sure Customers Can Checkout in the Meantime?
Create a backup calculated shipping rate and/or enable a different real-time shipping provider as mentioned above.
Can I Still Ship Via USPS?
Yes, of course, you can still create calculated shipping methods with the USPS names in the meantime. You could calculate shipping as a flat fee, a fee based on weight, based on total price etc.