A simple domain name reversal function.
$ curl https://rgee0.o6s.io/dymo -d 'rgee0.o6s.io'
io.o6s.rgee0
The function will also accommodate http:// and https:// schemes:
$ curl https://rgee0.o6s.io/dymo -d 'https://rgee0.o6s.io'
io.o6s.rgee0
And strip tailing paths:
$ curl https://rgee0.o6s.io/dymo -d 'https://rgee0.o6s.io/dymo/makes/labels'
io.o6s.rgee0