How to resolve "cannot add or update a child row: a foreign key constraint fails" in sql?

Example:

INSERT INTO orders (user_id, product) VALUES (999, "Book");

This error occurs when there is a violation of referential integrity due to a foreign key constraint.

Solution:

-- Ensure the foreign key value exists in the referencing table
INSERT INTO orders (user_id, product) VALUES (correctUserID, "Book");