What does reply path mean in relation to sending a text message?

Reply path refers to the message centre number that is used when a recipient replies to a text message that they have received from you. If reply path is ticked, the recipient will only be able to send their reply back to you using the same message centre number that it was received through. If this message centre is too busy at any time, you may have trouble receiving the text message.

If reply path is not ticked, it means that any replies to messages can be sent through any message centre.