There is a difference in how MLCS configurations are displayed between Server / Data Center instances and Cloud istances.
Server / Data Center
In Server / Data Center instances you can find the MLCS configuration in the Issue settings. To show the configuration, Custom Fields, click the wheel on the top right corner and click on Issues. Then, click on Custom fields to show a list of your custom fields. Click on the three dots and choose Configure context. The configuration will be shown under the voice “Options:”, here is an example:
Jira Cloud
In Jira Cloud, the configurations of your Multi-Level Cascading Select custom fields are stored in the MLCS app. To see and manage the configuration, click the Settings dropdown menu and click on Apps. Find “MLCS Cloud” and click on it. you will see the configuration with all your options. To connect a configuration to a Multi-Level Cascading Select custom field, click on the Element Root (the first level option) and assign it to your field.
