licensing – GPL API for Android Application

I would like to develop an Android app which will use APIs under GPL 3.0 Licence. To make sure that all the things were done all right, what do I have to do in my application? Do I have to mention the data source providing a link in an about page for example? Do I have to mention the APIs author?
Can I charge money for my application?

The source of my data will be a simple HTTP GET from a herokuapp link

Stay healthy and thank you!