I’m sorry for the delay in replying. I was doing some tests based on what you wrote and I have some great news.
As recommended, I switched to test in another OU and it worked. Thanks for the help, my problem solved.
Here is a comment that might help:
I do not know if it occurs in Microsoft AD, but in Samba 4 it does not work if you leave the “Organizational Unit” field empty. You can set the default “CN = Computers” or any other OU and the FGO Client will be able to join the domain, but using this in a blank option will give the error 87 even if you use “redircmp” to save to another OU.