httpRequest with two credentials - how to avoid insecure interpolation of sensitive variables?

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Hello,
I would like to understand how my code need to look like, so that I don’t see the warning:

The following steps that have been detected may have insecure interpolation of sensitive variables (click here for an explanation):
httpRequest: [BACKUP_PASSWORD]

The API of an non public application requests, that I authenticate against the API with Username and Password, stored in BACKUP_CREDENTIALS and provide an password (Secret BACKUP_PASSWORD) in JSON format in the request body.
When restoring the backup zip file, both credentials need to be provided again.

import java.time.*
import java.time.format.DateTimeFormatter

def timeStamp = Calendar.getInstance().getTime().format('YYYYMMdd_hhmmss',TimeZone.getTimeZone('Europe/Berlin'))
println timeStamp

pipeline {
	agent any
	
	stages {
		// https://www.jenkins.io/doc/book/pipeline/syntax/#supported-credentials-type
		stage('Backup') {
			environment {
				HOSTNAME = "example.com"
				BACKUP_PASSWORD = credentials('RESTORE')
			}
			steps {
				timeout(time: 120, unit: 'SECONDS') {
					script {
						// https://www.jenkins.io/doc/pipeline/steps/http_request/
						// https://plugins.jenkins.io/http_request/
						
		                withCredentials([string(credentialsId: 'RESTORE', variable: 'BACKUP_PASSWORD')]) {
		                    def response = httpRequest url: 'https://' + HOSTNAME + ':1234/api/backup',
		                    acceptType: 'APPLICATION_ZIP',
		                    authentication: 'BACKUP_CREDENTIALS',
		                    consoleLogResponseBody: false,
		                    contentType: 'APPLICATION_JSON',
		                    httpMode: 'POST',
		                    ignoreSslErrors: true,
		                    outputFile: BUILD_NUMBER + '_backup_' + timeStamp + '_' + HOSTNAME + '.zip',
		                    requestBody: """
								{"password": '$BACKUP_PASSWORD'}
							""",
		                    timeout: 120,
		                    wrapAsMultipart: false
		                }
					}
				}
			}
		}
	}
}

Thank you in advance.