For some reason I'm not able to create a Roll-Up Summary field n the Build a Lemonade Stand.  It's not even an option and scrolling over the help text, it says "You cannot create this type of field on this object because it is not the master in a master-detail relationship."  Not sure how this can be fixed?

For some reason I'm not able to create a Roll-Up Summary field n the Build a Lemonade Stand.  It's not even an option and scrolling over the help text, it says "You cannot create this type of field on this object because it is not the master in a master-detail relationship."  Not sure how this can be fixed?

For some reason I'm not able to create a Roll-Up Summary field n the Build a Lemonade Stand.  It's not even an option and scrolling over the help text, it says "You cannot create this type of field on this object because it is not the master in a master-detail relationship."  Not sure how this can be fixed?

• Create an OData 2.0 External Data Source named 'Mobile Devices' using the following URL: https://phone-odata-demo.herokuapp.com/devices.svc/
• Use the 'AtomPub' format and the 'Anonymous' Identity Type for the 'Mobile Devices' External Data Source.
• The 'Mobile Devices' data source must validate and sync the 'phone_plans' table to result in an external object with the API name 'Phone_Plan__x'.
• The 'Mobile Devices' data source must validate and sync the 'phones' table to result in an external object with the API name 'Phone__x'.
• Note that you will need to adjust the Object Names for the two external objects from the default setting after the initial sync.

all the thing have been done but i am getting following errorwhile checking challenge.