QVIS Remote Viewing on iphone and ipad by domain cctv

I have a QVIS zeus-8 channel dvr and I want to know how to remote view, I have a talk talk router and I know my ip adress and the dvr address.I tried once it worked then stopped so I got an engineer and asked him and he fixed it and I repested this more than once, just to let you know I already have a Dynamic dns ready and I have the remote viewing app ready which is the QVIS app and the other one is DMSS so I just want to know how to fix this problem and I dont want the engineer coming in again and just to let you know this is an ipyish domainish cctvish topic. Hope I get answers!!!