in my Github action I use a temporary variable for a timestamp and want to send this variable in a webhook, but github cant interpret the $var in string. Can someone pls help me?

The code looks like this:

- name: Posting Rocketchat
    if: failure()
    run: |
        TS=$(date  %Y%m%d%H%M%S)
        curl -X POST -H 'Content-Type: application/json' --data '{"text":"❌ Test: Leads Testing Desktop