Seamless procedural sphere with Simplex Noise

Good day, I apologize for my poor language (This is not my mother tongue and I’m just learning :))

I’m doing the procedural generation of the planet. I can write a cube, normalize it and even apply 3D noise Simplex. However, I am faced with problems - these are seams between the planes. There are no gaps, but shadows spoil the whole view.

I think the problem is in the wrong normalization. Since there are no so-called “neighbours” on the edge of my peaks. I was advised to add them, but I did not quite understand how it works. Some incomprehensible word for me, “average your vertices on the edges.” Can someone help me with this?

I can not solve the problem for more than two weeks.