It wasn't a plug in but a module comprising 2 php files uploaded to the plugins/deliveryLimitations/Client/ folder and 1 php file uploaded to the lib/max folder. It was from a company called adservermods.
Meanwhile, since we use device targeting constantly, I found a mobile targeting plugin from a company called reviveadserverplugin.com which seems to work well with 3.2.1
I am still trying to get an update from adservermods but so far the update they sent has not worked. Hopefully they will figure out a way to make it work on the new server. Their module doesn't offer targeting for specific mobile device types but is convenient for those campaigns that need generic targeting of desktop, tablet or mobile rather than more granular targeting.
Believe me, we truly appreciate the Revive Adserver because it offers a very elegant and efficient option without getting caught up in a very restrictive and costly ecosystem controlled by Google, Microsoft and a few other giants. We have been using OpenX and Revive now for over a decade.
I also understand the constraints under which the Revive team works, and I have tried to support it by buying plugins created by team members.
But several times a year we face situations when it would be nice to have more seasoned experts willing to provide prompt solutions or at least point us in the right direction so we don't have to devote so much time to trying to find solutions on our own. I am currently facing one of those situations. I was not able to get any help on this forum, so am now turning to others for help.
I like the Admin's suggestion of some kind of paid subscription-based premium service that would assure prompt, reliable support from a knowledeable team. I for one would support it, as long as the cost is reasonable.