Roman, in your HTML document code here:
http://prntscr.com/us1d7athere were such constructions
https://prnt.sc/us1aal ,
https://prnt.sc/us18u3 which "broke" the whole template and when creating a document, the system cannot create a "broken" document, as a result we get a 500 error.
Such constructions are transferred when copying a document, for example, from MS Word.
I fixed it and now it works.
For the future, I advise you to better make a document with 0 in the system using the tools
http://prntscr.com/us1d2g