The credentials provided for the Web source are invalid.

Hi Anonymous, late to the party, but I came across this thread when I recieved the same error and think I have a solution.

After a lot of messing around, I tried out the whole process on my work Desktop computer, rather than laptop. THe only change that I could percieve between the two is that the Desktop is connected to some kind of Ethernet Network, whereas the laptop was on a different WIFI Network that works for all other access/permissions for work. For whatever reason, I think that moving to the Desktop may have allowed me to slip through a firewall that my company has set up and let me make the changes. It's super strange as I haven't had any issue like that before now, but it's what worked for me. Perhaps changing WIFI or using a VPN may solve this issue for you?

Hopefully this is helpful, maybe you already managed to solve it another way, which would be good to hear about.