Minecraft Lighthouse keeper Success?

Maybe someone can help… And although yesterday I tried to get the success lighthouse keeper and have also looked at me 2 tutorials on Youtube, I did everything as in the tutorials, but I still did not get the success.

Built the pyramid from iron blocks. Starting with 9x9 then 7x7 then 5x5 and finally 3x3 blocks and in the middle the beacon placed.

I play on the Xbox One.

When the whole thing is standing and then light up a block and put it back. That always triggers success for me. I've never got that different.