vCenter Orchestrator HTTP API: POST Request Error 400 1032

I am trying to start a workflow via a POST request to the vCenter Orchestrator API. When I run the same workflow with a GET request, there are no issues and I get the following output in the localhost_access_log.current_date.txt:

[src_ip_address]- - [13/Oct/2015:04:46:00 +0000] "GET /vco/api/workflows/af83cf34-6a00-45b5-946e-0d44ece508bb/executions/ HTTP/1.1" 200 272

However, when I run a POST with the following parameters:

restMethod: POST

restEndpoint: https://[dest_ip_address]:8281

restPath: /vco/api/workflows/af83cf34-6a00-45b5-946e-0d44ece508bb/executions/

user: [username]

content: {"parameters":[{"name":"name1","type":"string","value":{"string":{"value":"value1"}},"scope":"local"}]}

contentType: application/json

accept: application/json

I receive the following error in localhost_access_log.current_date.txt:

[src_ip_address]- - [13/Oct/2015:03:53:39 +0000] "POST /vco/api/workflows/af83cf34-6a00-45b5-946e-0d44ece508bb/executions/ HTTP/1.1" 400 1032

And the output on the client side:

{Success=no, ResponseHeader={null=HTTP/1.1 400 Bad Request, Server=Apache-Coyote/1.1, Content-Length=1032, Content-Language=en, Connection=close, Date-Tue, 13 Oct 2015 Message=Bad Request, ReasonPhrase=Bad Request, StatusCode=400}

I am running vCenter Orchestrator 5.5. There is no output to the server.log file. I haven't had any luck researching the '400 1032' error number. [dest_ip_address] is HTTPS. Can anyone help clear this up?