For users on paid plans, most unsubscribe requests like Stop, Opt Out, Unsubscribe, Take me off list and a few profanities are automatically unsubscribed by the SMS platform. The accounts on Free plans need to unsubscribe contacts themselves since the SMS platform does not action them.
You can unsubscribe OptOut requests manually as below.
1/ Click on CONTACTS > Batch Unsubscribe > Type in / copy paste the numbers to unsubscribe into the box > Unsubscribe these mobile numbers.
2/ Click on the CONTACTS > View > look up contact > click on the number/name > Tick Inactive > Update Contact.