UPU terminal dues were up for renegotiation in 2018-2021 anyway.[1] That's done every 10 years. The end result of all the noise from the US seems to be the same thing as would have happened anyway - a rate change in 2021.

The UPU classifies countries by level of development, and there's a price break for underdeveloped countries.[2] China is currently in group 3, along with Chile and Lebanon, and was probably going to move up to group 2 in the 2021 round anyway.

So all this was mostly hype.

[1] http://www.upu.int/en/activities/terminal-dues-and-transit-c...

[2] https://www.uspsoig.gov/sites/default/files/document-library...