The "Check_in_Date_c__c" field doesn't exist on the "External_Reservation__c" object, or you don't have access to the field.

Hi @Lisandro Gabriel Cacciatore

I am from the Trailhead Help Team. Can you please confirm if you're still seeing an issue? If Yes, please let us know so that we can go ahead and create a case on behalf of you and can assist accordingly. 

Thank you!

++TrailheadHelpFollowUp