First, check the customer record's Activity tab — every request shows a delivery status (sent, delivered, failed, bounced). A failed SMS almost always means the phone number is missing a country code or is a landline.
Bounced emails usually mean a typo in the address or a full inbox on the recipient's side — Sadakom surfaces the bounce reason returned by the mail provider directly in the activity log.
If status shows delivered but the customer says they never got it, ask them to check spam folders (email) or verify they haven't blocked your sender number (SMS).