Slack notification action missing when creating a new alert

My Slack integration is working for only 1 project in my account. More specifically, I have 2 projects under my account. When I try to create a new alert for the first project I see the “Send a Slack notification” in the actions dropdown menu. However, I don’t see it when I do the same for my second project. My first project is a python project (scrapy spider) and the second is a Django project.

Does anyone know why this is happening? I am currently using the free tier account.