When using package manager with sources which require to authenticate yourself (e. g. internal sources or paid subscriptions), it may happen that you need to change your password or just entered the wrong credentials.

Now, it is kinda like 'evil', because you do not get prompted again. The invalid credentials are saved and you are just lost seeing error messages the whole time.

Following solutions are available:

• Remove the source from Visual Studio, close, open, enter them again (works 2 of 4 times)
• Go to Control panel - User Accounts - Manage your credentials and check if they are listed there (never had that...)
• Update the credentials with dotnet:

list all and update afterwards:

dotnet nuget list source
dotnet nuget update source "<source name>" -u <username> -p <pass>