How to add field validations or make specific fields mandatory

Summary:

How to add field validations or make specific fields mandatory

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Our operators need to capture certain extra data in WMS so the system can send proper EDI messages to our customers in background interfaces. Some of these informations are stored in custom fields, but these are not mandatory and not validated by the system. If a user fails to follow the instructed steps, the EDI interface lacks information and fails as a result. How can we make the solution more fool-proof, e.g. by adding validation logic to these fields? The only technique our integrator has proposed is to validate these fields in OIC, and send out an email if there