Cast error on REST API /91/replication/symmetrix/{symmetrixId}/rdf_group

I tried to create the RDF Group via the RestAPI on Ansible Tower, the code is show below.

When we run the job, it always return the error message:

"com.emc.em.domain.symmetrix.om.datamodel.facade.SymFibrePortFacade cannot be cast to com.emc.em.domain.symmetrix.om.datamodel.ISymRDFPort, status code was 400"

I already tied to replace the variable to a static value and test again, but the same error flow. 

"portNumber" : 4

We confirmed that the Port and Director ID are valid and online. Is there any special format I need to use to pass the Port value via RestAPI?

uri:
url: "https://{ {Var_UnisphereIp}}:8443/univmax/restapi/91/replication/symmetrix/{ {Var_SymmID}}/rdf_group"
method: POST
return_content: yes
status_code:
- 200
- 201
url_username: smc
url_password: "{ {Var_mypass1}}"
follow_redirects: yes
force_basic_auth: yes
validate_certs: no
headers:
Content-Type: "application/json"
body_format: json
body: {
"label" : "{ { Var_RDFGroupName|upper }}",
"local_rdfg_number" : "{ { Var_RDFGNumber }}",
"local_ports" :
[{
"symmetrixID" : "{ { Var_SymmID }}",
"directorId" : "{ { item.value.Var_Dir }}",
"portNumber" : { { item.value.Var_Port }}
}],
"remote_rdfg_number" : "{ { Var_RDFGNumber }}",
"remote_ports" :
[{
"symmetrixID" : "{ { Var_RemoteSymmID}}",
"directorId" : "{ { item.value.Var_Dir }}",
"portNumber" : { { item.value.Var_Port }}
}],
"metro_witness" : "{ { Var_Metro_Witness_bool }}",
"executionOption" : "SYNCHRONOUS"
}