ReadyNas 528x - Using TimeMachine feature with Mac

I have a ReadyNAS 528X running Firmware 6.10.1 that is connected to a domain. This is primarily a Windows enviroment however, we have 6 Macs that we need to back up user documents that are not stored on the server. For the Windows computer we use OneDrive's back up tool, however there is not the same functionality for OneDrive on MacOS. So we decided to use TimeMachine (which is a feature on the NAS). Five of our six Mac's work fine with connecting to the NAS and backing up. However, we have one that says "You do not have the necessary read, write, and append priviliges on the selected network backup disk.". Keep in mind this is connected to the domain so credentials have to be the same for connecting to the NAS as it is the server and have verified those are correct. When I put the right password in I get that message, when I put the wrong password in it doesn't give me that message. This is a Mid 2015 Mac with Retina and running macOS Mojave 10.14.6. 

However, on the same computer I created another TimeMachine account on the NAS and used it to connect and it worked fine. It seems to be this one account. Looking for any help. Have already checked all permissions and can see the backup disk for that use account. Have tried deleting it and recreating it and still have the same issue. Also reach out to Apple and after the steps they walked me through they said it was probably the on the NAS. 

Thanks in advance.

Edit: This is a private Time Machine setup.