I read the following post
This is exactly what I need for my application. At the end of the post I read that the Geospatial Search is in alpha stadium but the post is already one year old.
I cannot find any information about the status of Geospatial Queries at Google App Engine. Is it still in Alpha stadium or can I use in production?
so for everyone who is interested in: today 27. Jan 2017 Geospatial Queries are still in Alpha stadium.
You need to create a search index of mode geospatial for your Geo Point Property and this is not allowed