You must sign up for a free account on http://back4app.com in order to create a App on back{4}app, grab its App and Client Keys and paste them the Configs.swift file of this app.

back{4}app service offers the following FREE features for the STARTER pack:
• 1 GB Database Storage
• 5 GB File Storage
• 10 Requests/second
• 50 K Requests/month
• 1 Cloud Code Job

Check out its PRICING tables here: https://www.back4app.com/pricing/

Here you can find DOCS: http://docs.back4app.com/

That’s a bug of Xcode 8 with macOS Sierra, check this sample video to see how to fix it: https://youtu.be/z2LemT1_LqA