Rate limit errors from sonatype

We are consistently getting 429s from sonatype in a private repo:

> Could not GET 'https://oss.sonatype.org/content/repositories/snapshots/org/rundeck/rundeck/3.1.1-SNAPSHOT/rundeck-3.1.1-20190911.182503-15.pom'. Received status code 429 from server: Too Many Requests

Potentially an IP white-list issue?