Graylog Sidecar Fail Register 403 error

## Context

I have sidecar running inside a docker container and it works fine for all but a few instances. For those servers where it does not work it's throwing the following error:
```
time="2019-12-02T22:38:53Z" level=info msg="node-id file doesn't exist, generating a new one"
time="2019-12-02T22:38:53Z" level=info msg="Using node-id: c8ccb4d0-8e1a-4d49-b088-0c06882ceb87"
time="2019-12-02T22:38:53Z" level=debug msg="Creating rotated log writer (10/10) for: /var/log/graylog-sidecar/sidecar.log"
time="2019-12-02T22:38:53Z" level=info msg="Starting signal distributor"
time="2019-12-02T22:39:03Z" level=error msg="[UpdateRegistration] Bad response from Graylog server: 403 Forbidden"
time="2019-12-02T22:39:13Z" level=error msg="[UpdateRegistration] Bad response from Graylog server: 403 Forbidden"
```
The config file looks like this:
```
server_url: ${API_URL}
server_api_token: ${GS_API_TOKEN}
tls_skip_verify: ${GS_TLS_SKIP_VERIFY}
```
The start script looks like this:
```
#!/bin/bash
rm -rf /var/log/graylog-sidecar
/usr/bin/graylog-sidecar -c /data/collector_sidecar.yml
```

## Expected Content
It should start up without the 403 forbidden error

## Your Environment
Graylog Version: 3.0.2
Sidecar Version: 1.0.2
Filebeat Version: 7.4.2