I was testing escher, using the documentation form here: https://escherauth.io/escher-js.html

The documentation is wrong, because if I add the 'X-Escher-Date' header, it'll be in a wrong format, and the PHP implementation is not accepting it. If I do not add this header, the library generates it in a correct format.
The other error is, that I had to add the 'host' header too, it's not in the example.