SSM Composite Doc RunShellScript Fails

I have created a composite SSM document that included the AWS-RunShellScript document: This is the action portion:

{
  "action": "aws:runDocument",
  "name": "RunShellScriptHello",
  "inputs": {
    "documentType": "SSMDocument",
    "documentPath": "AWS-RunShellScript",
    "documentParameters": "{\"commands\":\"echo hello >

/tmp/testcomp"}" } When I run it, I keep getting the error: Invalid format in plugin properties map[id:0.aws:runShellScript runCommand:echo hello > /tmp/testcomp timeoutSeconds:3600 workingDirectory:];

error json: cannot unmarshal string into Go struct field RunScriptPluginInput.RunCommand of type []string

I just don't understand why I am getting this response.