The error points to a missing input variable
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Thank you so much. everything works 
Hi , can you show how you set that up in the BP? I’ve been looking for something to make that work.
Recommend if you find this thread to use ViewportUVToSceneTextureUV instead of ViewSizeAndInvSize as Suggest by @DotBow. When UE uses a ScreenPercentage lower than 100 you get weird picture in picture results from masking.