The most common way to stop receiving texts from an automated system is to reply with the word STOP. Some businesses also allow other phrases, like QUIT, OPT-OUT, Unsubscribe, cancel, etc. Unless the entity texting you directs you to use one of those phrases, your best bet is to use the word STOP.
Opt-out example Not choosing to subscribe to newsletters, unticking a previously ticked checkbox, not consenting to save personal details, rejecting the use of cookies, etc. are some examples of opt-out. E.g. Companies add an unsubscribe link at the end of their emails to let users opt out of emails.
Example STOP (opt-out) messages: "Company-Name: You have been opted out and will not receive any further messages".
The key component of a clear opt-out text message includes clear instructions on how to opt out, including opt-out keywords and sending the customer an unsubscribed confirmation text. For example, “Reply STOP to unsubscribe.”