It seems like you are experiencing an issue with importing Spine 4.3.14-beta exported data into Unreal Engine 5.5.4 using the spine-runtimes-4.3-beta plugin. The error message suggests a version mismatch, but since you've confirmed that both the plugin and the exported data are version 4.3, the issue might be related to the file naming convention or a specific setting during export. Make sure that your asset files do not share a common prefix, as this can cause issues in Unreal Engine 5.3 and later. For example, if your files are named skeleton.skel and skeleton.atlas, try renaming them to skeleton-data.skel and skeleton.atlas. Additionally, ensure that the "Premultiply alpha" setting is not enabled in the texture packer settings, as this is not supported by the spine-ue4 runtime.

We had a similar issue a few weeks ago.

Since the v4.3 Editor is still in beta, it means that not all runtimes might be updated to support v4.3 exports yet. This issue sounds exactly like the one we ran into, except in Unreal rather than Unity.

I recommend you use v4.2 until v4.3 is released out of beta, since that will ensure your exports and imports all work properly from the Editor to the Engine.

The runtime changes in 4.3 are pretty big and still in flux. As such, porting from the reference implementation (libGDX) to C, C++, etc. will only happen once the reference implementation has stabilized.

Vein Make sure that the prefixes of the .atlas and .skel files are different. This is a required step for using UE 5.3 and later versions. For more details, please refer to the following section in the documentation:
https://esotericsoftware.com/spine-ue#Updating-to-Unreal-Engine-5.3-