If you’re using an Alphanumeric Sender ID (Custom word) as your Sender ID, it is impossible to receive replies as there is no reply number associated with the SMS.
A valid number needs to be set as a Sender ID to receive replies. If you require replies to your messages, please use an alternative two-way compatible Sender ID, such as a Virtual Number or one of SMSGlobal's Shared Numbers.
To receive replies from your recipients, please refer to the article what can I use as my Sender ID ‘From Address’ for two-way communication?