I have/had created a shared file and given read/write permission to Admin.
My problem is accessing the HD I have attached.
On a Mac, in a Finder window, I follow the path: Network/SynologyRouter/Connect as, I get "Enter your name and password for the server "Synology Router".
My assumption is that it is asking for the credentials I use to access the Synology Router Manager but it rejects those credentials and I haven't a clue as to what userID and password it is demanding.
Yes...on any server, you must input the credentials of the server. Apple makes this less than clear by filling in the user name. Unless they are exactly the same, remove the user name prepopulated in the Apple connect box. Often folks leave the name there...thinking it is correct, or, they put in the PW for the name in the box....which is wrong.
One way to prevent this inconvenience is to use
exactly the same admin name and PW on both devices (Mac and NAS). Obviously, this is less secure. If anybody knows the credentials, they can access both machines.
Otherwise, delete the always-filled-in user name and type in the credentials to the admin account on the Synology.
Other tips:
Don't use the default admin account Synology, as every attacker will try the known, default user name. Then they only have to guess the PW. Much easier than discovering both. Create a new user, and give it a unique name, and admin rights. Log in as that user, and make sure everything is working as expected. Once well tested and confident, you can remove admin rights from the default admin account, or delete the account completely.