Could you please explain the difference between the GrowthBook API and SDK? Which one is better to implement on my site? Also, I have a second question: how can I define backend A/B testing? I don’t want to change the visuals of my site. Every fifth user transaction on my site currently gives a bonus, but I want to test if giving a bonus on every third transaction would change user behavior. Could I set up this experiment in GrowthBook (the code for this feature is written in the backend), and should I use the API or SDK for this?

The API is used to interact with the features and experiments stored on GrowthBook. The SDK is used to parse the feature and experiment values by your code, to assign users and log the exposures

Many thanks!