If you want to update the set of properties (not just one) that's how it's done:
Let's assume that you have a Thing:
It has several properties:
By creating a real PUT request:
with following headers:
appKey=<yourAppKey> (for testing purposes you should create one with Admin as user reference, not a good idea in a production scenario though)
with following body (raw):
if you choose a Content-Type=text/xml
than your body must be as follows:
<prop1> awesome text </prop1>
If you (or your App) cannot create a PUT request, than you need to append in URL '&method=put' in regular GET request, but you need to check
Allow request method switch in your PlatformSubsystem configuration (Platform will treat this GET request as it would be a PUT request). This will make you expose to risk of CSRF of coarse.
If you are creating a GET request you should send the values in URL - that is not recommended through several reasons, technically it is possible to pass data in Body even with GET request (HTTP 1.1), but HTTP handlers do not handle those data same way as they do with other requests.
I hope you will find that useful.
If yes mark this answer as correct.