Problem: I have a Form that creates new posts in a custom post type. One of the custom fields holds a telephone number. I would like to prevent the Use from creating a post if the telephone number they submit already exists in the database as a telephone number for another post.
Solution: Use the Forms API hook cred_form_validate to inspect the submitted custom field value. Create a custom post query that also queries posts by that custom field value. If any posts are found in that query, display an error message on the telephone field.
Relevant Documentation:
https://toolset.com/documentation/programmer-reference/cred-api/#cred_form_validate
