I have reviewed other posts related to Data Modeling Challenge and cannot figure out why I received the error message: Challenge not yet complete in Custom Object Playground tlg We could not find a custom object 'Offer__c'.

Hi @Terry Givens

Please check whether the tab setting on profile is set to "Default On" and Check if the Object permission checkboxes are checked for the profile (Read/Write/Delete/View All/Modify All). 

If they aren't checked, then check the boxes as per your business requirements.