Nodejs-Sequelize insert into join table many-to-many

I set up two models in sequelize that have a many-to-many relationship. Sequelize created the join table correctly, but I'm not able to insert into it. I've been poring over this section of the docs: https://sequelize.org/master/manual/advanced-many-to-many.html but I can't get anything to work based on their examples. They don't have a many-to-many example, unfortunately.