Getting {"error":"invalid_grant","error_description":"authentication failure"} in Salesforce?

I am trying to get the Session ID for my salesforce partialbox.

My Code:

curl https://test.salesforce.com/services/oauth2/token -d "grant_type=password" -d "client_id=definitely the correct client id" -d "client_secret=definitely the correct client secret" -d "username=mymail@mail.com.partialbox" -d "password=passandsecuritytoken"

What else I did:

• Grant full access in my connected app settings
• Set Ip restrictions to loose ip restrictions
• "All users can authorize themselfes"
• Double checked pass, client id, client secret, username

I am still getting the error {"error":"invalid_grant","error_description":"authentication failure"}.

I searched through the SF forums and Stack Overflow questions, but I couldn't find any solution for this. Does anyone know, what else could be the problem here?