First step is to check the client profile and can see the client was sent a reminder and you can see they were sent a reminder
If the reminder is showing here then this means we have sent it our end. However there are a number of cases where a 'sent' text doesn't always arrive.
Unfortunately this is down to the individual network provider. Slick can only guarantee the sending off the reminders and not the safe arrival.
Below is the list of common reasons a network such as O2 says they might not be able to deliver a message:
The number might be on roaming mode or might not be connected to the network e.g turned off, out of signal
Operators are also known require SMS services to re-route the message via another working route, which can cause temporary delivery issues.
The client might have put the number in the Do Not Disturb list
The carrier might have technical difficulties