List the messages already in use
Your billing platform, subscription app or support team may each send different messages. Before adding another reminder, write down which tool sends each one, what event starts it, who receives it and where the message record is kept.
Record what happened
Keep the notice type, related offer or subscription, planned date, actual send time, channel, message copy and source. If the system reports a delivery result, save that too.
Queued, sent, accepted, delivered, bounced and opened are not interchangeable. Keep them separate and do not infer a result you cannot see.
Review late or unclear records
A date may have passed, a source may be missing, or two systems may disagree. Preserve those facts and ask someone to review them. Do not make a late notice look timely or treat a missing message as proof that none was sent.