Two listen path to be used

Thank you Olu for the quick response. I have a doubt regarding the regex solution you pointed out. Could you please help? the link is It's possible to use regex in the listen path?

Why test: is present in listen path regex? Could you please help here understanding this. Thanks in advance.
"proxy": { "listen_path": "/v{test:[\d]+}/events/", "strip_listen_path": true }