If the command text you are sending does not start with '[' and end with ']', they are not an array.

[Link: jsonrpc.org]

It may be that KODI does not yet support this feature as I see your URL has request={some json body for single request}. If this is indeed the case, you will be faced with sending multiple HTTP requests and processing responses asynchronously to get a User interface that flows well and is considerate of socket resources.