How to solve the problem with no token found when connecting a new target in Prometheus?

Question

Monitoring

Hello.
Registered a new target in prometheus.yml

- job_name: some_metrics
    metrics_path: /metrics
    static_configs:
      - targets: ['server01:8001']

restarted Prometheus, checked via API
server01:9090/api/v1/targets
error returned

"labels":{"instance":"server01:8001","job":"some_metrics"‌​},"scrapeUrl":"serve‌​r01:8001/metrics","l‌​astError":"no token found","lastScrape":"2017-12-19T12:15:20.826915394+03:00","h‌​ealth":"down"}]}

How to solve this problem?