Since August 2022, Ready Player Me no longer supports exporting avatars as FBX files. It’s still possible to convert a GLB avatar file to FBX manually using Blender.
https://docs.readyplayer.me/ready-player-me/integration-guides/unreal-sdk/blender-to-unreal-export
Export FBX from Blender
- Download the avatar .glb file.
- Open Blender on an empty scene.
- Select File>Import>GLTF 2.0 and then select the .glb file you downloaded.
- Wait for the import to complete and the model to appear in your Blender scene.
- Select File/Export/FBX. The Blender File View window opens.
- Notice the Operator Presets on the right.
- Adjust them as shown in FBX Export Settings below.