Thanks for posting your code!
For finding your IP address on Heroku, I was originally thinking you could just do something like,
heroku run -a my-app "curl https://ifconfig.me/", but when I tried it, I realized that the IP address was different each time, and anyways it wouldn’t necessarily be the same as the IP address that that app itself connects from.
Right now my best guess is that our IP rate-limiting code is being triggered because there are so many users connecting from the same set of Heroku IP addresses. We’re currently working on debugging this issue, thanks for your patience!
I am glad to hear that deploying on Digital Ocean seems to fix the problem.