Ok, so on your interface, you have the check box for "Validation". However, in my case. there is not option of "Validation check box" somehow even if I use the version 10.8 of Enterprise GDB.
Yes, I published as editable feature service. The validation rule was successfully configured and saved it before publishing it. Also, all other required configuration were matched in accordance with ESRI doc.
Also, I have tested to publish the data as editable feature service with "Calculation rule", and this worked fine. I also tested the validation rule for the data in FGDB, and it worked fine as well.
The data that I am trying to publish is Annotation feature class - is this a problem by any chance??