Using variable in jenkins file for robocopy command - jenkins

Question

I am writing a Jenkins pipeline script to copy files from the source to the destination folder. The only difference from lots of articles I already visited is that my source and destination paths are not fixed but constructed using variables. I have a very strange issue that the variable names are used instead of their value, have been trying since the whole day. My Jenkins script is below
pipeline
{
agent any
parameters
{
string(name: 'SPRINT_NUMBER', defaultValue: '', description: 'Sprint Number')
}
environment
{
DESTINATION_PATH=""
SOURCE_PATH=""
}
stages
{
stage('Copy')
{
steps
{
script
{
/* APPROACH-1*/
DESTINATION_PATH="C:\\Release\\" + "${env.SPRINT_NUMBER}" + "\\" + "${env.BUILD_NUMBER}" +"\\Destination"
SOURCE_PATH="C:\\Source\\bin"
echo "DESTINATION_PATH: ${DESTINATION_PATH}"
echo "DESTINATION_PATH: ${SOURCE_PATH}"
/* the below doesnt work, echo prints correct DESTINATION_PATH and SOURCE_PATH though*/
bat '(robocopy ${SOURCE_PATH} ${DESTINATION_PATH}) ^& IF %ERRORLEVEL% LEQ 1 exit 0)'
/* APPROACH-2*/
bat label: '', script: '''Set src="C:\\Source\\bin"
Set dest="C:\\Release\\${params.SPRINT_NUMBER}\\${BUILD_NUMBER}\\Destination"
/* the below doesnt work, the variable name used instead of values*/
robocopy %src% %dest%'''
}
}
}
}
}
The Console out put from Jenkins is
For first approach
7:00:58 -------------------------------------------------------------------------------
17:00:58 ROBOCOPY :: Robust File Copy for Windows
17:00:58 -------------------------------------------------------------------------------
17:00:58
17:00:58 Started : Tuesday, July 28, 2020 5:00:58 PM
17:00:58 Source : C:\Program Files (x86)\Jenkins\workspace\CopyFilesJob\${SOURCE_PATH}\
17:00:58 Dest : C:\Program Files (x86)\Jenkins\workspace\CopyFilesJob\${DESTINATION_PATH}\
17:00:58
17:00:58 Files : .
17:00:58
17:00:58 Options : . /DCOPY:DA /COPY:DAT /R:1000000 /W:30
For second approach
17:00:58 -------------------------------------------------------------------------------
17:00:58 ROBOCOPY :: Robust File Copy for Windows
17:00:58 -------------------------------------------------------------------------------
17:00:58
17:00:58 Started : Tuesday, July 28, 2020 5:00:58 PM
17:00:58 Source : C:\Source\bin\
17:00:58 Dest : C:\Release\${params.SPRINT_NUMBER}\${BUILD_NUMBER}\Destination\
17:00:58
17:00:58 Files : .
17:00:58
17:00:58 Options : . /DCOPY:DA /COPY:DAT /R:1000000 /W:30