It's in this text on the page:
If you are using a “FYSETC mini12864” please review section 3.3 of the FYSETC Spider documentation (https://voron.link/m6wtwnl).
Note: I just did a search for voron.link within the PDF and tested all the links, the rest are currently working.
1) Link on page 121 doesn't work due to a space in the text of the link after link/
2) On page 248 of the Assembly Manual one of the links is broken. https://voron.link/m6wtwnl
It's in this text on the page: If you are using a “FYSETC mini12864” please review section 3.3 of the FYSETC Spider documentation (https://voron.link/m6wtwnl).
Note: I just did a search for voron.link within the PDF and tested all the links, the rest are currently working.