here’s the thing about game dev: there’s always something new to learn!
The way that the ‘white’ top output on the texture sampler works is it only combines the red, green, and blue channels. that bottom output, alpha, isnt included there (dont ask why). to fix this, you’d have to add an ‘append’ node out of the top output and plug in the bottom alpha output in to the append to bring all 4 channels (r,g,b,a) in to it.
but i would suggest not doing that, as that doesnt help you here.
what you’ve done, is plugged the colours in to ‘base colour’, but base colour doesnt define opacity only colour. you need to put the opacity channel in to the opacity or masked inputs on the material. (opacity is a sliding scale of see-through to opaque, while masked is solid/invisible)
but the opacity/masked inputs are greyed out, meaning you havent set the material to be translucent or masked.
also: for me, ive always had trouble getting alpha channels to work with PNGs, I always prefer to use .TARGA or .TIFF files for this instead, especially if I’m exporting them out of Photoshop. this is to do with how files are compressed in UE4. the way .PNGs work, is they don’t really (afaik) actually have an alpha channel, they just treat a ‘null’ colour value as opacity. This means they wont work in UE4, because you actually need an alpha channel to get it to work properly.
i hope this is understandable.