Unfortunately, it is not possible to transfer games or add-ons across separate platforms. You will be fully responsible for any costs incurred by moving to a new platform. This is an industry standard and not something we have any control over.
Furthermore, we have no involvement with the financial side of your purchases from these platforms, as such you should refer back to the retailer you purchased from, if you have a query about your purchase. The following are separate platforms with their own storefronts.

Platforms:
  • PlayStation
  • Xbox/Microsoft Store/Game Pass for PC
  • Steam (PC)
  • Epic Games Store (PC)

When you purchase an add-on or game from one of these platforms, you acquire a licence to use that content solely on the platform it was bought from. Consequently, you are bound by the terms and conditions established by the platform provider (e.g., PlayStation). These game licences are not transferrable to other platforms for competitive reasons.

To use a real world example: "Buying a ticket for one airline won't get you a seat on a different airline's flight"

The sole exception lies with Microsoft, who endorse cross-buy products. These products can be used across all Xbox and Microsoft Store platforms, where the product explicitly states that it is compatible with Xbox One, Xbox Series S|X and PC platforms.

Example: