I will illustrate my problem with an example.
In WordPress I have a custom post type called Mission Definition.
I defined a mission with the following specifications
– first name and last name : Matin
– Mission Start Date: 2020-01-14
– Mission End Date: 2020-01-20
And I saved this mission, then I want to make a new one.
I want no mission in the name of Matin to be saved from date 2020-01-14 to date 2020-01-20 and give an error.
Thank you for solving my problem.
I have attached a photo of the fields for you dear friend.
You need to create an acf/validate_value (https://www.advancedcustomfields.com/resources/acf-validate_value/) filter. For example you can add the filter on the name field. In the filter you need to get all of the values you are validating on and then do a query to see if there is existing posts with that value. In the past I posted an example of doing this here https://support.advancedcustomfields.com/forums/topic/accept-only-unique-values/#post-45359