SpongeForge breaking Pixelmon on Proxy

Trying to get Pixelmon Modpack to be avaliable on my 1.20 proxy server through ViaVersion & ViaBackwards.
As far as I understand SpongeForge is required to allow this, however adding SpongeForge to the server makes tcg.main and pixelmon.main get rejected in the vanilla acceptance check. Relevant log error posted.
Any known fixes?
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