Asus OpenVPN Server Static IP
For me, it looks like you gave the client config file (nuc) the wrong name. OpenVPN works this way, that each of the possibly very many clients can have its own config - and the config file for one specific client is distinguished by the Common Name of the Client, as the common name is unique.
If your client's common name is tester as you write, you have to rename the client config file inside the ccd directory to tester, and it should work...