V-Bucks purchased on Nintendo Switch and PlayStation are only available on the platform they are purchased on. V-Bucks purchased on the Epic Games Store will be available on all platforms except PlayStation and Nintendo Switch.
This means your V-Buck balance may change depending on what platform you’re on. Examples are below:
The restrictions outlined above apply to V-Bucks only. Any content purchased with your V-Bucks will be available across platforms. For specific details please visit the Official Fortnite FAQ.