I am adopting sfdx. And development was quite easy and straightforward. But the problem take it place when I've started to use packages. A version and package itself are both created successfully as well as deployed and executed. But I'm not able to make any change in my production org even though the package's type is Unlocked. An error message saying me that "managed installed class cannot be saved"
So..What's my problem and what's my option to do here?
Here is my sfdx-project.json. Just to make it's clean, that I didn't use namespaces