When importing new shipping rates into Magento 2 using a .csv file into the table rates method, I received the cryptic error;
something went wrong
I had previously hit upload_tmp_dir errors, but this was much easier to solve.
Just export the current values and make sure the headers match to the import .csv. This often happens if you switch from weight to subtotal, or vice versa, to calculate the shipping cost.
The Magento 2 shipping .csv is slightly different to the import used in Magento 1, with the ‘Delivery Type’ column no longer needed.
I think I was just missing the Zip/Postal Code column.
I hope that helps!