How to pass variable as Input Parameter to BuildMatser Deploy Package Rest API?

Hi
I am trying to pass VAriable as Input parameter to Deploy Package Rest API. I have created a Json object having all parameters which i am passing as -body for Deploy Package API like below:
$DeployPackageParams = @{releaseNumber=$ReleaseNumber;
packageNumber=$PackageNumber;
applicationName=$ApplicationName;
key=$APIKey;
$FileType="Config";
}
$DeployResponse = Invoke-RestMethod 'http://BMServer/api/releases/packages/deploy' -Method Post -Body $DeployPackageParams
I have created a variable with FileType name in BuildMaster Application. But during deployment this FileType variable is not getting assigned with passed value. How to assign parameter value to local application variables in Buildmaster plan ? I have tried same by using querystring as well but no use.

Product: BuildMaster
Version: 5.7.2

You are using it correctly; there is a bug in that particular endpoint that ignores the variables for non-legacy plans, see: Issue BM-3077