Because a REST request is a URL, there can be no spaces between the parts of a
request. A browser will stop reading when it runs across the first space. For
example, if the last parameter read, Keywords=Blue Shirts, the request
would end on "Blue." "Shirts" would never be
read. If you have key words, such as names, that do have spaces in them, you must
URL-encode the space using %20. For the preceding example to work, you would include
a URL-encoded space, as follows.
Keywords=Blue%20Shirts
The same problem occurs if you put spaces between the parameters in a request, as
shown in the following example.
SearchIndex=Apparel& Keywords=Shirt
In this example, the request would end with "Apparel&."
Often, this kind of mistake returns an error because parameters required by the
operation are not read. So, make sure to remove all spaces within a request.