This Concert Window was rockier than most. My comments didn't show up in chat -- return / enter did nothing, just a newline. (Tried cmd-enter, option-enter, ctrl-enter too -- all the same.)
And I could not tip. Clicking the button crashed the window -- said to try the Back button. Fine. But no tip.
On a Mac, tried in both Safari & Chrome: same.
Sorry you had trouble. Make sure you aren’t running any add blocking or pop up extensions in your browser as they can interfere with the chat functionality.