Ue4 float3 and float4 are undefined SM5

When I try to change the preview weight I get this error as you can see in the stats.

Please tell me how to fix it and make sure to break down your explanation step by step so I can understand clearly please I know to ue4 so yeah.

Haven’t worked with landscape materials (and that node in particular) but I’d say you need to use alpha here rather than RGBA which is a 4 vector. It’s almost too small to read but where it reads Height (?) I’d just plug A (alpha) - that’d make way more sense than RGBA.