@PhilipDAth is correct. To further the answer, it's because when performing the GET request, you're getting all attributes of the SSID - some of which are NULL as they have not been configured or are not applicable/configurable. When sending that configuration back into a PUT, you're sending NULL values for attributes which are NULL by default but require a valid value for configuring (or are not configurable) - hence "radiusFailoverPolicy' must be a string" You'll need to parse out some values from the GET request (such as NULL's) and ignore them rather than trying to send them into the PUT request.
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