try like this?

infrastructure/ddns/cronjob.yaml

@@ -22,16 +22,16 @@ spec:
                 &&
                 curl https://ntfy.kluster.moll.re/kluster_ip
                 -H "Title: Kluster IP"
-                -d "Currently: $(CURRENT_IP)"
+                -d "Currently: $CURRENT_IP"
                 &&
                 curl
                 --request PUT
                 --url https://api.cloudflare.com/client/v4/zones/$(CLOUDFLARE_ZONE_ID)/dns_records/$(CLOUDFLARE_DNS_RECORD_ID)
                 --header "Authorization: Bearer $(CLOUDFLARE_API_KEY)"
                 --header "Content-Type: application/json"
-                --data '{"content": "$(CURRENT_IP)", "name": "$(KLUSTER_DOMAIN)", "proxied": false, "type": "A"}'
+                --data '{"content": "$CURRENT_IP", "name": "$(KLUSTER_DOMAIN)", "proxied": false, "type": "A"}'
                 &&
-                echo "Updated $(KLUSTER_DOMAIN) to $(CURRENT_IP) successfully"
+                echo "Updated $(KLUSTER_DOMAIN) to $CURRENT_IP successfully"
 
             env:
               - name: CLOUDFLARE_ZONE_ID