How Do I Run A Php Script Without Actually Opening It

I want the PHP script to run at regular intervals (2 months).

For example: Let’s say I run some kind of business where I receive a specific amount of money every 2 months. If I get the payment in the time frame then it’s fine but, if I didn’t receive payment, then the script should send me an email.

I don’t want to open the webpage and allow the script to check and notify me, that’s time consuming. A real world example is IFTTT.