How to assign issuees different issue type schemas to issue types within the same project

[Deleted user]

We have a running project in Jira.

I added a new issue type which and a new issue type schema for the issue type

I would like to associate the new issue type schema with the project, however when I try to do this, I received a warning saying:

All selected projects will change from their current scheme to the selected scheme. Any issues with obsolete issue types will need to be migrated.

Errors

There are 768 sub-tasks that will be affected by this change. You must have at least one valid sub-task issue type.

Is it not possible to have different issue type schemas for different issue types?

[Nic Brough -Adaptavist- · Accepted solution]

No.  An issue type scheme is a list of possible issue types, which doesn't make sense when applied to an issue type. 

The issue type scheme tells a Jira project what issue types are available to be used in the project.  You can have many different issue type schemes, and each project can either share one or have its own.

The error you are seeing is because you are changing an issue type scheme to say "do not allow any sub tasks in the projects this scheme is used by", but you have some sub-tasks existing in the projects.  Jira will not convert sub-tasks automatically, you will need to either provide a sub-task type in the new scheme so it can move the existing sub-tasks to that, or convert, move or delete the existing sub-tasks.