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Check if you forgot to set the "data" field inside your request. If you did set it, check if it's being serialized before sending, and if it's being serialized the right way.
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com.fasterxml.jackson.core.JsonParseException: Unrecognized token 'Hello': was expecting ('true', 'false' or 'null')
at [Source: java.io.StringReader@4983a458; line: 1, column: 6]