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Hello there, I need help with my iPhone 6s. Almost Everything in this phone has been replaced but I am still running into the issue of error nine when restoring on iTunes. The weird part is when I went to restore it in a cold environment it restored but then got stuck on a boot loop. Sometimes it gets further restored more than other times but usually ends up crashing or getting stuck in a boot loop. I keep getting error 21 and Error 9. Does anybody know why this might be?

Try this. https://support.apple.com/en-us/HT201444