Installation:

1. Unpack callbackevent.zip
2. Move the folder into /wp-content/plugins
3. Activate the Plugin "CallbackEvent" in the Backend
4. In the Sidebar of the backend appears "CMB Settings"
5. There, you have to insert 3 Values: CliendID, ClientSecret, CalendarID and, if you like, change the default Thank-you Text :)


Create ClientID & ClientSecret
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1. https://console.developers.google.com
2. "Create Project"
3. Go to the Menu APIS & auth => Credentials
4. On the right side unter "OAauth", press the Button "Create new Client ID"
5. Chose "Web Application"
6. Fill in the address of your page under "AUTHORIZED REDIRECT URI".
7. After a few seconds, the data appears, including ClientID and ClientSecret

CalendarID
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1. https://www.google.com/calendar
2. Create a calendar, e.g. "Callbacks" and go to it's calendar-settings.
3. In the settings-page, paragraph "Calendar Address", there is the calendar id.
4. The calendar id has the form "rih2k42k4jh24kj24h24kh2@group.calendar.google.com"

Insert the 3 Values you got in the steps above into the Form and press Save.

Afterwards, a link "Authenticate" appears. Click that link, to authenticate at google-services.

That's it!

To show the callback-form in your page, use the "[cmb]" shortcode.

Now, if there is a request, it automatically appears as an event in your created "Callbacks" Calender at Google Calendar
and you can setup up your smartphone or similar to remind you.