Is anyone else experiencing this?

We havent changed our code but the authentication is failing now. I believe it's something that we need to configure in our Salesforce instance but I do not know what is misconfigured. 

We are using Oauth2 password grants and .Net framework 4.6 so it is using TLS 1.2. There are no ip blocks. Can anyone provide tips on what we should be looking at next? Thank you in advance for all the help!