
Hi,
How are you connecting to CRM online is it through User Name and password?
Can you confirm if the user through which you are connecting to CRM does not have MFA enabled. See below article.
Turns out I was using an older version of the Microsoft.CrmSdk.CoreAssemblies nuget package(7.1.1 in one project and 8.0.0 in another) as soon as I updated it to the latest (8.2.0.2) I was able to successfully connect to CRM Online.
Check if you are using latest version of sdk packages.
The error "An unsecured or incorrectly secured fault was received from the other party" usually means that the password is incorrect, but it can also occur if the time between the application and the CRM server is more than 5 minutes apart.