"tox: command not found" despite tox being present in the active environment

[native-api]

          Was getting error message like:

pyenv: tox: command not found

The `tox' command exists in these Python versions:
  2.7.18
  3.7.17/envs/project-tools
  project-tools

Note: See 'pyenv help global' for tips on allowing both
      python2 and python3 to be found.

The project-tools is a customized version of python in our company.
I ran this command before the tox command:

pyenv activate project-tools

Originally posted by @monicaluodialpad in pyenv/pyenv#92 (comment)

[native-api]

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