UID is the abbreviation for Unique ID, which is for accessing your Reolink camera/NVR. With UID, username (which is admin by default), and password, you are able to access your Reolink camera/NVR wherever you're.
So where you can find UID? Here introduce some methods you can locate your UID.
UID on Camera body/NVR box
UID is printed out on a sticker which is pasted on the camera body or NVR box.
For Argus, UID can be found on the back cover and the others can also be found on camera body:
If you purchased a Reolink NVR, the UID is on the NVR box upper plate:
UID on Reolink App
UID can be also found with Reolink App under the premise that you ever logged on to the camera/NVR on Reolink App. It doesn't matter whether you are able or not to access it for now.
Go to Device Settings (the gear icon) >> Share, and you'll see what is same as printed out on the sticker.
UID on Reolink Client
You can also find the UID on Reolink Client.
step a. Find your camera/NVR on Reolink client and click to enter "Devices Settings" page.
step b. Find "Advanced" and click it to the next page then you will find the UID.