TOPIC: DT Register Google Cal Export error : redirect_uri_mismatch

Hello
And sorry for my bad english
I try to install the plug-in for Google cal Export. I see the video (poor text quality, impossible to read, just listen). I follow the instructions and I have the green button Google Cal Export but after pushing en Event, I receive an error message
"The redirect URI in the request: http://www.pnlformation.ch/plugins/syst ... th_api.php did not match a registered redirect URI

scope=https://www.googleapis.com/auth/calendar https://www.googleapis.com/auth/calendar.readonly
response_type=code
redirect_uri=http://www.pnlformation.ch/plugins/system/google_auth_api.php
access_type=offline
display=page
prompt=consent
client_id=123456789.apps.googleusercontent.com (I change the number)

Someone can help me please, I'm newby
I work with Joomla 1.5.26 (I try to move to 2.5)
Thanks