In a few days USPS is changing it’s service methods and rolling the “First Class” method into “Ground Advantage”: https://www.usps.com/ship/ground-advantage.htm
Does anyone know if we need to change anything in CS-Cart for shipping rate calculations to keep working?
I think the usual practice in such cases is to leave the old services running for some time, to let the companies change their systems. So I don’t think there’s anything to worry about - if anything happens, you can always contact with CS-Cart support and they should be able to assist you 
Best regards,
Robert
ACK! The USPS Ground Advantage went into effect and the First-Class Shipping Calculation BROKE! We have thousands of vendors in our marketplace using First-Class shipping.
This is a major issue for any CS-Cart customer using USPS shipping methods.
Confirmed, First Class Mail is not working and yes this is an issue for us as well.
Thank you for letting us know. I stumbled across this thread while checking the forum, and added this to our short-term development plans. Ideally, we’d like to include it in version 4.17.1 (scheduled for release in a few weeks), or 4.17.2 at worst.
This is an urgent fix that we need as well. First Class mail was the cheapest shipping option and waiting several weeks isn’t acceptable because we lose orders due to available shipping options being too expensive. Could you create a patch we can use in the mean time? Especially if we’re not ready to do an entire store update.
Thank you for bringing this up!
It’s too soon to say for sure, but we’ll consider it. First we’ll need to actually implement USPS Ground Advantage. If we can provide a solution for older versions of CS-Cart, it will most likely be done through our Customer Care service.
Our developer already fixed it in one day.
That said, I know not every CS-Cart user has there own developer. So I hope CS-Cart fixes it quickly for them. It wasn’t difficult to add Ground Advantage to the list of shipping services.
Would you be kind enough to share the actual fix here? I just edited the DB to change First Class to Ground Advantage and it did not work. It must be something very simple, but unless it is exactly what USPS wants it will fail.
For the thousands of users who got blindsided by this, you will need to update the database as well as the Usps.php file:
First the database tables:
cscart_shipping_services - find the once where code is ‘First Class’ and change it to ‘Ground Advantage’
cscart_shipping_service_descriptions - Find the row where ‘description’ is USPS First Class Mail and change it to ‘USPS Ground Advantage’
Then the app file:
www/app/Tygh/Shippings/Services/Usps.php
First make a duplicate of this file in case something goes wrong, but this is the file that needs to be edited. Lines 487, 488, and 490, and 643. Change all instances of First Class to Ground Advantage, and match the upper/lower case of what you are replacing.
That should do it - it worked for me.