I have completed trialhead certification on Salesforce Platform Basics Badge, is there any validity for this certification and I have added it in LinkedIn profile. Please advise as I'm new to Salesforce.

Hi All, 

Im trying to do the second challenge in App Customization  but am getting some Super badge am getting the error "Challenge Not yet complete... here's what's wrong:  Couldn’t find the 'Volunteer Shift' relationship field or it is not configured correctly."
Please, anyone, can anyone tell me which relationships should be created between these objects? I have created a master-detail relationship between them. 


Also, am not clear with this "Shifts with cascading delete and the option of roll-up summary fields." 

Thank you and any help is appreciated.
Thank you in advance.