I checked your dashboard and saw that your station sent data for 11 minutes from 09:13 - 09:23 pm on Apr 25. Then it stopped.
Maybe now, with adding the "?" it stopped ?
Things may have changed at the pwsweather end meanwhile (or between a GW1000 and a HP2551, see end of post).
"Initiating" at PWSWeather only means that your data is being checked by PWS quality control during 5 days for being considered consistent.
However, as they use a content management provider, the update only happens (+/-) every 5 minutes (probably with the update interval you chose; i.e. if you chose 60 seconds, every 5 minutes five 1-minute records will be added). At the very start this delay can be bigger.
Your upload without the "?" may have been successful, only you didn't see it yet - and adding the "?" interrupted it.
And you misinterpreted the "initiating" status (which is still on, by the way).
I suggest you start over (in the sense, remove the "?" from the path end, save and wait for an hour and then check your station dashboard again. It may just work... (re-checking the API key would also be an option - such a long string invites potential typos ...)
The "?" may still be needed, but it's worth a try. The HP2551 console may work slightly different in its posting from a GW1000 with which the tests of the thread you refer to was performed. While the HP2551 has separate WiFi and console firmware, the GW1000 has a "combined" firmware.