Create or Update All Substitution Variables Defined for the Application

Hello,

I am trying to leverage "Update Substitution Variables " REST API and below is the code:

Through Postman it is working fine.

I am trying to execute it as I did for Business Rules, Data Maps.

I am new to groovy. I am not sure, if I am doing it in the right way.

def updatesubs =
{
"items": [{
"name": "Test_CurYr",
"value": "FY23",
"planType": "ALL"
}]
}

HttpResponse<String> jsonResponse = operation.application.getConnection("connectionname").post("/rest/v3/applications/applicationname/substitutionvariables")
.header("Content-Type", "application/json").body(updatesubs).asString();

I am getting the below error:

"Error:The Groovy script failed to compile with internal error: Compile Error: