ANYONE PLEASE ANSWER ME WITH THIS ISSUE: My phone still in Limited Warranty and there’s problem on the phone screen

So apparently my phone is now in iStore Philippines try to check what’s the problem of my iphone 13 with purple vertical line on the edge of the screen. And it’s already 4days since my phone was still at istore and they said if they cannot fix the phone. They will deliver it to manila or HK,

my question is if the problem is the screen, do I need pay for it even if I still have limited warranty? Because there’s no dents and cracked to my phone. I never drop the phone in the water or floor. The purple line accidentally appear while using the phone. This is the issue, a purple line