FailedToDeserializeDatasetError using Push Datasets Api

Hello,

I am sending a request like this:

I followed the instructions from the post dataset documentation referred here:

https://docs.microsoft.com/en-us/rest/api/power-bi/pushdatasets/datasets_postdataset

The testDataset is the one from the site, literally copy and pasted, and I keep getting this 400 bad request error:

There is not a lot of information about this error on the web. Please, could anyone help me?