Advanced Formulas : Use Basic logic in checkbox Formulas : Create a validation rule indicating

Advanced Formulas : Use Basic logic in checkbox Formulas : Create a validation rule indicating whether an opportunity has a closed date in the past.
The validation rule should be on the Opportunity object
The validation rule should be named 'Close_Date_Alert'
The validation rule should fire if IsClosed is not selected and CloseDate is yesterday or earlier
The validation rule should display the error 'Hey McFly, unless you are planning to go back in time, please update your close date' at the top of the page when triggered

Complete trailhead challenges solutions for Admin Advanced
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[atharv]

Sir, TYSM for these videos. I am new to this technology, pls can you tell me why this trailheads are used means what r advantages of this and what is main purpose of this?? and also what is connection of CRM and salesforce

[jonathanteixeira]

Well, it tell me "We tried to create an opportunity with tomorrow as the CloseDate, but we couldn’t. Make sure the validation rule fires only when the CloseDate is in the past." I dont know why

[viswachaitanya]

Pleasedo the Module:External Services:Use External Services in a Flow