Hi @Farclaimer28022935h3cf,
Thanks for the message.
From your picture, it seems your UVs are beneath the UDIM 1001. Substance 3D Painter can paint only on a positive space tile (on the right or the top of the UDIM 1001).
I'd advise you to relocate all your UV shells on the tile 1001 and to reimport your mesh in Substance Painter.
Best regards,