We can’t find the merge field {!$Input:Contact.Next_Check_in_Date__c} in the prompt template. Hello Community, In the "Craft an Effective Prompt Template", there is no " Next Check-in Date " merge field in my org. What should I do? Thank you!

My issue is resolved with following steps 

Under Agentforce studio -> Agentforce Agents -> Toggle "Enable the Agentforce(Default) Agent" 

Fyi