I'm having an issue when I try to execute a CURL command in one of the steps of a Jenkinsfile when it's working behind a proxy.

I'm working on Ubuntu 18 and I run the Jenkins container in like this:

docker run -d
-u root --privileged 
-v jenkins_home:/var/jenkins_home 
-v /var/run/docker.sock:/var/run/docker.sock 
-v "$HOME":/home
-e JENKINS_OPTS="--prefix=/jenkins" 
--group-add 997
-p 8080:8080 
-p 50000:50000 
--name jenkins 
jenkinsci/blueocean

And then I have a simple Jenkinsfile that clones the code from a git repository, makes an image, pushes it to a registry and finally sends a Telegram message using curl.

pipeline {
  agent any

  environment {
    dockerImage = ''
  }

  stages {
     stage('Testing') {

      steps {
        echo 'testing'
      }
    }

   stage('Build image') {
      steps {
        script{
          dockerImage = docker.build("registry.***.com.ar/hellonode")
        }
      }
    }

    stage('Push image') {

      steps{
        script {
          docker.withRegistry('https://registry.***.com.ar', 'registryCredentials') {
            dockerImage.push("${env.BUILD_NUMBER}")
            dockerImage.push("latest")
          }
        }
      }
    }

    stage('Push Notification') {
        steps {
            script{
              
              withCredentials([string(credentialsId: 'telegramToken', variable: 'TOKEN'),
              string(credentialsId: 'telegramChatId', variable: 'CHAT_ID')]) {
                
                sh '''
                curl -s -X \
                POST https://api.telegram.org/bot${TOKEN}/sendMessage \
                -d chat_id=${CHAT_ID} \
                -d parse_mode="HTML" \
                -d text="