I have a problem when I downgrade my phone to ios 15.6

"There was a problem downloading the software for the iPhone “iPhone”. The requested resource was not found."

I had trouble with my Mac when I was trying to restore my iPhone. Can anyone help me? And then I researched on gg, I found this, I tried to follow what the video said, but it still doesn't work. After running the process, my phone is still on ios 16.

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