Why is Greenlight asking me to authenticate my purchase?

Great question! 

Some merchants request additional authentication to confirm that you’re the authorized cardholder before completing a purchase. This involves sending a one-time verification code (OTP) by text message to the phone number associated with your Greenlight account. 

If a merchant asks you for additional authentication, just enter the OTP on the merchant’s website, and you will be able to continue with your purchase!