Time Machine Server

I’m having issues connecting my Macbook pro to time machine external drive. Currently my the time machine external drive is connect to my mac mini which Im trying to use as a time machine server. Ive given it a static ip address and have turned on file sharing on the mac mini. However, every time I try to connect to the drive over the network I get a error. ” There was an error authenticating with the provided username or password. ” But I am able to connect via vnc and smb to mac mini and see the time machine the external drive on the Mac mini but can not use it as a time machine backup.