How to pass file parameters to upstream pipeline job in build step plugin

Question

def BUILD_USER = currentBuild.getBuildCauses('hudson.model.Cause$UserIdCause')
pipeline {
    agent {label "master"}
    parameters {
        string(name: 'BUILD', defaultValue: '123')
        booleanParam(name: 'Deploy', defaultValue: 'true')
        booleanParam(name: 'Upgrade_Config', defaultValue: 'true')
        booleanParam(name: 'SchemaComparison', defaultValue: 'false')
        booleanParam(name: 'Publish_Server', defaultValue: 'false')
    }

    stages {
        stage ('Start Deployment') {
            agent {label "master"}
            steps{
                script{
                    sh '''
                        rm -rf /params/parameters
                        cd /params
                        echo $BUILD_USER
                        python3 buildParameters.py --Build=$BUILD --Publish_VM=$Publish_Server --userName=BUILD_USER --Upgrade_Config=$Upgrade_Config
                '''
                file = readFile('/params/parameters.txt') 
                }
            }
        }
        stage ('UpgradeConfigurations') {
            when {
                expression { params.Deploy == true }
            }
            agent {label "master"}
            environment {
                          file = "${file}"
                        }
            steps{
                script{
                    println("${file}")
                build(job: 'UpgradeConfigurations', parameters: [ file(name: 'parameters', file: "${file}"), string(name: 'build_uniqe_id' , value: "${BUILD_USER}") , booleanParam(name: 'Deploy' , value: "${Deploy}") , booleanParam(name: 'SchemaComparison' , value: "${SchemaComparison}")], propagate: false, wait: false )

               }    
            }
         }  
    }
}

buildParameters.py file generate some additional parameters in parameters.txt file on master vm and I am trying to pass it to the upstream job UpgradeConfigurations

Upstream job UpgradeConfigurations is getting started but file parameters are not getting passed as parameters to it.

I have tried using base64file as well but no luck.

Referred Build Plugin doc: https://www.jenkins.io/doc/pipeline/steps/pipeline-build-step/