getting 500 Internal Server error for Email API using Rest API Explorer

HI Team,

I am getting 500 Internal Server error while sending Email API through Rest API explorer. Can you please let me know that Am I missing any configuration changes or any setting needs to enable or header related input at the time of calling Post Email API ?

Raw output:- 

{
  "error": {
    "message": "org.codehaus.jackson.map.JsonMappingException: Can not deserialize instance of java.util.ArrayList out of VALUE_STRING token\n at [Source: com.glide.size_aware.SizeAwareServletInputStream@ba2498; line: 1, column: 2] (through reference chain: com.glide.email.service.Email[\"to\"])",
    "detail": "Can not deserialize instance of java.util.ArrayList out of VALUE_STRING token\n at [Source: com.glide.size_aware.SizeAwareServletInputStream@ba2498; line: 1, column: 2] (through reference chain: com.glide.email.service.Email[\"to\"]) Check logs for error trace or enable glide.rest.debug property to verify REST request processing"
  },
  "status": "failure"
}

Regards,
Manish