FHIR server: logical reference that makes <HSFHIRErr>MalformedRelativeReference

"basedOn" : [{
    "reference" : "CarePlan?identifier=urn:ietf:rfc:3986|urn:uuid:3aae92e6-9c51-46ab-83bb-bc3a5a66d429"
  }],

Hello,

I am new to InterSystems FHIR server implementation and in process of evaluating it. (R5)

I try to create a Task referencing a CarePlan resource as above.

I got the following error message and I wonder what could be the mistake as it used to work against another FHIR server implementation. (the referenced CarePlan resource does not exist but I guess that in this case the error code would be different?)

{
  "resourceType": "OperationOutcome",
  "issue": [
    {
      "severity": "error",
      "code": "invalid",
      "diagnostics": "<HSFHIRErr>MalformedRelativeReference",
      "details": {
        "text": "The reference value 'CarePlan?identifier=urn:ietf:rfc:3986|urn:uuid:3aae92e6-9c51-46ab-83bb-bc3a5a66d429' in property (basedOn) of Type 'Task' is malformed"
      },
      "expression": [
        "Task.basedOn[0]"
      ]
    }
  ]
}

Regards.