Check these two attributes on your PL/SQL process in the dynamic action:
Page items to submit - sends data from the browser to the database
Page items to return - any session state updates you made in PL/SQL can be reflected in the items on the page.
Your problem relates to the latter, though after posting I realise you may be talking specifically about dynamic actions handling popup mechanics.
Check the sample dialog application, you'll probably find your answer there, or supply more information about what you have here.
I have similar question.
I use apex.server.process to call AJAX Callback Process. In this PL/SQL code i use APEX_UTIL.SET_SESSION_STATE to set value of item. And it works correctly ofc.
How to update item value after call in this case ?
There is no "Page items to return" field in AJAX Callback Process.
And if i try to get value by $v("ITEM") after process call, i get old value.
I found this site and it works pretty well.
I have been converting my codes now to use this since it allows so much flexibility.