Landscape RestAPI error – Invalid API version
Quoting from the documentation
The version of the API, 2011-08-01 being the current one
You might want to read that documentation carefully as your query seems to miss some parameters (signature method, version and timestamp). Also, your parameters need to be sorted.
We were able to resolve this issue by creating a URL-encoded value from the Base64 value.
We intend to use Powershell to perform all of these different types of encoding automatically, once we have identified which calls to make to gather all required data about devices and the hardware and software that is installed on them.