Hello everybody ,
I am working on D365O update 3, and trying to set up a field based security privilege, the concerned form is CustTrans(Customer Transactions), First i used the standard MS privilege CustTransMaintain to test so i created a security role (TestRole) and assigned to it the two privileges (CustTableView) and (CustTransMaintain).
The user i used to test has only standard system user and TestRole assigned, when i press edit on a customer transaction i can modify some fields and some others not.
The requierement is to remove the ability to update some of the updatable fields .

Lets take the Document field(CustTransTable_DocumentNum) for example, in order the achieve that and based on the this MSDN documentation for AX 2012. i just customized the CustTransMaintain privilege as the following:
Effictive acces on CustTrans Entry point from delete to update:
Direct access permission created for Table CustTrans with EffictiveAccess set to update and under it added the field DocumentNum with EffictiveAccess to read.

I restarted all the server due to data cash conflicting possibility, but i still can modity the field.
Play on AllowEdit value for me is not an option.
Thank you for your time.