Regular Expression working on regexr but not in PHP

Hello, i want to use regex to validate the coupon format. I wrote the rules on regexr.com and it worked fine but not in php.

The expression i have: ([0-9]{3})+(-)+([0-9A-Z]{3})+(-)+([A-Z]{3})

Coupon format:

230-4WE-GAG

424-423-NJB

Basically the first 3 digits are numbers followed by a dash then 3 alphanumeric digits followed by a dash and at the end 3 characters

And the code i have:

PHP Code:

if (preg_match('/([0-9]{3})+(-)+([0-9A-Z]{3})+(-)+([A-Z]{3})/', $coupon)) {            
     $coupon_data = $this->coupons->check_coupon($coupon);
     $this->response($coupon_data, 200);
} 


(i'm using the rest library)

I know that PHP treats regex a little bit different but in which way?