Slack can't find all users or channels

I am unable to find all channels and people with the slack integration. Even if I put it in manually it looks like it crashes “Testing data failed. Please ensure that the settings are correct or try again.” I have tried with channel name and channel ID. Please help!

Did you figure this out? I am facing a similar where I have set up everything but slack app does not show any channels under it, even tho i integrated the app in alot of channels