pbx () { curl -sF "c=@${1:--}" -w "%{redirect_url}" 'https://ptpb.pw/?r=1' -o /dev/stderr | xsel -l /dev/null -b }

What does the 'r=1' do? Can you tell me where this is documented?
Also, are you sure you want to send the output to /dev/stderr when xsel is expecting input from the pipe?

Please direct me to a more appropriate (IRC?) support channel if this is not the place to ask.

Using the pattern in the examples on the website, MultiBar::listen will likely hang if an error occurs as the ProgressBar::finish function will never get called. It'd be nice if listen would stop blocking if there aren't any more progress bars.