JSON update error

Hello!
Thanks for support!
WordPress 5.8.1 and here we use both the classic editor and Gut in it. and here is an error in it when saving http://clip2net.com/s/4fEX9pn
The standard solutions did not solve the issue, these are changes in the rest api https://c2n.me/4fEXkpN.png and in the security plugin