How to pass variables in TemplateBody section of Cloudformation

Im trying to pass RegionName in the TemplateBody section but getting the error as "Template format error: Unresolved resource dependencies [RegionName] in the Resources block of the template".

Here is the yaml file which I'm using:

      TemplateBody: |
        Resources:
          CWEvent:
            Type: AWS::Events::Rule
            Properties:
              State: ENABLED
              Name: Rule
              Targets:
                - Arn: !Sub "arn:aws:events:${RegionName}:1234:event-bus/My-Bus"
                  Id: 'Event'
                  RoleArn:
                    !Join
                      - ""
                      - - "arn:aws:iam::"
                        - !Ref "AWS::AccountId"
                        - ":role/"
                        - "Role"
              EventPattern:
                source:
                  - "aws.ec2"
                detail-type:
                  - "AWS API Call via CloudTrail"
                detail:
                  eventSource:
                    - "ec2.amazonaws.com"
                  eventName:
                    - "RestoreSnapshotFromRecycleBin"

Also I cannot use S3 due to restriction so TemplateURL is out of picture.

If you used the !Sub function it should fill in all your variables for you, so your TemplateBody line should look like

  TemplateBody: !Sub |

This would then fill in your variables before the stack is deployed, you might need to remove the other !Sub's you have inside the template for this to work.