How to consider opt in for marketing message or how long will its hold

Hi, I’m new to this
I have build an API and using it. No issues on utility message. But when I try marketing message, its work fine yesterday due to I have reply message to opt in. But on today it’s no longer able to receive anymore until I message the business number again. Is the opt in message only last for 24 hour? Or that not consider opt in for marketing message?
Thanks for the help.