Retrieving an API key
To access photos from Pixabay you need to create an account or log into your Pixabay account.
Visit this link in the API docs of Pixabay. In the key parameter you will either see a Login | Sign Up action ....
...or the API key when you are logged in.
Accessing High-Resolution Photos
In order to get access to high-res photos instead of low-res(around 640px x 540px) photos, you have to ask for permission. Therefore visit this link and next to the headline click on "requires permission".
After that a modal will appear. Check all checkboxes and explain the purpose of using Pixabay high-res photos, e.g. "I am selling business cards and want to give my customers the possibility to access photos from Pixabay....".
Lastly you have to wait 24-48 hours for the e-mail of Pixabay with the confirmation state.
Entering the API key
You only need to enter the Pixabay API key in the General Settings of Fancy Product Designer. If you have access to high-res photos, you can also enable the relevant option "Pixabay High-Res Images".
The API key needs to be set in the plugin options. For high-res photos you need to set pixabayHighResImages to true in the plugin options.