When I go to the oTree hub, heroku Projects. I see: "This app's oTree version needs to be updated before this page can be viewed". 
I have updated oTree (now 6.0.15), reloaded my projects on Heroku, and reset databases. But I still have the same problem. 
Can anyone help me? 
Thanks!

Disclosure: I built TreeHost, so take this with that in mind - but I ran into this exact problem before building an alternative.

This is a known pain point - oTree Hub/Heroku requires you to stay in sync with their infrastructure updates, and when something breaks it's hard to debug because you don't control the stack.

If you want to skip the Heroku dependency entirely, TreeHost (https://www.treehost.io) might be worth a look - you just upload your otreezip file, or zip up your oTree project and upload it, and it provisions a fully isolated environment with Postgres, Redis and HTTPS automatically. No Heroku account, no Procfile, no version mismatch issues. Works with oTree 5.x and 6.x. Free tier available, just launched.

Still worth debugging Heroku if you want to stick with it - the "oTree version needs to be updated" message usually means the Hub dashboard is enforcing a minimum version. Double-check that your requirements.txt has the updated oTree version and that Heroku actually re-deployed with it (check the build logs). A full git push heroku main after updating requirements usually clears it.