Setting up a Facebook App ID is really easy. Please note, You do not need to do this if you are using the (generic link) domain.
Log in and Go to http://developers.facebook.com then click on "My Apps", then "Create App".
A pop up should appear where you can enter the display name and contact email address. Then click "Create App".
Now select the 'Build connected Experiences' option and then click continue:
Now fill in a few details as shown below and be sure to choose 'Clients' as your App purpose.
Click "Settings" on the left panel and then select "Basic".
Now scroll down then select "+ Add Platform" & choose the "Website" option.
Now enter the domain you used for the Snappic gallery in the white-label settings in the "Site URL" section and click save changes.
Now enter the domain you used for the Snappic gallery in the white-label settings in the "App Domains" section and click save changes.
Next you can select a category (You can use the Business and Pages option)
Now click the toggle button next to "Status: In Development". It will ask if you would like to switch modes and you can agree to proceed.
Lastly, copy Your App ID and paste it in under the White-label settings on the Snappic portal where it asks for the Facebook App ID.