It means that if a user can execute a microflow in any way, you must configure a module role which has access to this microflow.
To do this, you can go to the microflow (double click on the error message), right click on the canvas, select properties and then under the title Security, you can edit the allowed roles. Alternatively, you can configure this through the module's security menu.
For all Microflows and Nanoflows that you create, it will be necessary to point out which Module Roles will have permission to access that flow.
This configuration can be done in the Properties tab > Security > Allowed roles > Select Module Roles.