pull-review: Keep failing to get pull request

Hi, I’m using pull-review in server mode with Hubot, but everytime I trigger the pull-review it always throw this error either it from slack, github, or CLI mode. I’m using my github personal access token as PULL_REVIEW_GITHUB_TOKEN with required permissions (repo, user)

  pull-review started on https://github.com/myrepo/all/pull/2556 +0ms
  pull-review Error: Failed to get pull request: https://github.com/myrepo/all/pull/2556
  pull-review     at /usr/lib/node_modules/pull-review/src/generate-plan.js:72:13
  pull-review     at process._tickCallback (internal/process/next_tick.js:178:7) +46s

The PR is in our private repo. Can you point out where I should fix this?