I am trying to make a pull request for the first time with Bitbucket, but I get an error.

Error message

The following error () occurred when saving the pull request.


・ Unrelated branch

Steps taken
  1. Commit and push a branch with SouceTree
  2. Select a newly created and pushed branch from "Create pull request" of Bitbucket, request destination is master
  3. Enter a comment etc. and create "pull request"->error

The branch you pushed shouldn't be irrelevant, but is there any possible cause?

I tried searching on usage sites and error texts, but I couldn't find it.