Before using Facebook buttons you need to set your Twitter application credentials.
To create a Facebook App, go and visit: http://developers.facebook.com/
Note: You need to use a personal Facebook Account for creating an App. A business account won't work. Your personal account needs to be a verified Facebook account. If your account isn't verified yet, you'll receive a text message from Facebook to verify your account. So make sure, that you have a mobile number set within your account, otherwise you won't be able to create an App. On Facebook Developers page, click on Apps at the top right hand side of that page and login to Facebook if you haven't done already. If you're on the App page click on "+Create New App" at the top right hand side. A new window will pop up (see image below). Enter a name for your new app, choose an App Category and click on Continue.
When you create a new App, Just remind that you must have to enter namespace minimum 7 letters, and all fields are require. After enter all field click "Create App". It will popup a window of Security Check shown image below, click on Continue.
Now you have successfully created a Facebook Application and you should be redirected to the Application page which should look like the one on the image below:
Note: Your newly created Facebook Application will be in Sandbox Mode as default. To get the App Live, click on Status & Review > "Disabled" . See Image Below:
You must have to enter canvas URL and site URL to post on facebook. For Add Url go to settings > Add Platform. It will popup a window as below image. In that Add "App On Facebook" and "Website".
once you click on "App on Facebook" and "Website" you will see the page as mentioned in the image below:
Within the Application Info make sure, that you enter the correct URL of your "Site URL" and "Canvas URL" and the URL does match 100% the one from your website. So if the URL of your website does include the www like http://www.domain.com than you need to enter it like that. If the URL of your website doesn't include the www, than you don't need to include the www within the URL. It's important that the entered Website URL does match the one from your actual website, otherwise the App won't work correctly and it will show an error message when you or your users try to connect with the App.
If you want to use your own Logo or image for the Application, you can do that by clicking on the app details menu > logo options. There are 2 options logo and icons. After clicking on any options, you'll get open popup. Click on the choose sign and upload your custom image/logo/icon for the App. We recommend that you're using a custom image for your App. This will give more trust and does look more professional when a user does connect with your Facebook Application. See Image Below:
Now, Click on the Dashboard menu and copy and paste the App ID and App Secret Key as below image:
Place them into the plugin settings page within the Facebook fields as shown in the image below:
Important: When you copy and paste all the needed IDs and Keys, make sure, that you don't have any empty spaces, either at the beginning nor at the end of these entries. If you have any empty spaces, then the Application won't work and will show an error message when you try to connect to the App. Click on "Save Changes".