Haoyu Peng

Hi @zimeg, thanks for confirming this issue as a bug. I think one simple fix can be replacing https://github.com/slackapi/python-slack-sdk/blob/7e3ab80cdfc4c257c2b46b630546d38920502064/slack_sdk/oauth/installation_store/internals.py#L38 with ` result = target_type(dt.replace(tzinfo=timezone.utc).timestamp()) ` according to the python doc:...