Using GET was simpler, but required everything to be on the URL
and URL encoded. There is a limit to the number of chars.

Using a POST message allows for longer but also fits in with the
ability to extend later with different features.

Right now, Windows, iOS and Mac Catalyst use a POST with a body, but
Android is limited and has to use a header. In future, switching to
a [JavascriptInterface] may be worth investigation.

Fix the tests

whatever mac

no idea

some ws

Some versions of Android fail with missing headers