How often should I get Botox? I'm curious about the frequency.

I am becoming very worried about my square jaw, so I am considering getting Botox.

My friends and I are getting this procedure done casually because it is so popular these days, but I heard that you need to get it done regularly to maintain the effects, so I decided to ask this question.
I am curious about how long the effects of Botox usually last after a single injection, and how often people get them. Does the duration of the effect or the recommended treatment frequency vary depending on the area being treated?
I looked it up online and heard that if you get it too often, you might develop a tolerance and the effect might decrease over time, so I felt unnecessarily anxious.
To ensure safe and effective results without developing resistance, it seems important to optimize the Botox injection schedule. Typically, what is the most appropriate interval for follow-up treatments?
I would also like to know if I need to get vaccinated again after the effects have worn off due to missing a treatment cycle, or if it is better to get them consecutively before the effects disappear.