I have not had any luck in the past year trying to get VDP backup to work reliably.
can anyone tell me what I might be doing wrong ?
You're not doing anything wrong. VDP is (was) not a very good product, primarily owing to the fact it's based on Avamar. At this point, though, salvage your losses and pick another data protection product which is both more robust and has a lifespan, because VDP is dead. A community favorite here is Veeam and it seems to be the defacto standard in protection of vSphere and Hyper-V workloads. There are of course others, however.