itunes won't accept my password

I am trying to log into itunes on my Mac. A pop-up comes up asking for my apple ID login. Each time I enter my (correct) password, it just asks again/ doesn't accept the log in credentials. My iphone works just fine with my apple ID. I went to appleid.apple.com and tried to reset my password and log on there. It sent a verification code to my phone, I typed that in on the website, and again I can log in there too. I typed in the new password on the popup for itunes, but it still won't accept my login. What am I doing wrong??? If I can log in on other websites/devices, but I can't log in on itunes, does that mean something is wrong with itunes, or is it something with my credentials???