Denphal disease!

[Brazilin]

Hello, guys.
Im here to ask if you could help me to identify what is happening with my denphal. It has 3 flowers oppened wright now, im using a fertilizer for roots 1 time per week and watering every two days. It gets direct sunlight from 7 to 11 AM. Im doing something wrong?
Also, its summer here in Brazill.

[james mickelso]

If it has spread, I would cut off the end of the leaf down to below the area in question and dab the cut end with powdered cinnamon.

[CPKidofAugusta]

How long has it been in that position? Could just be sunburn....

[Brazilin]

Well, after analyzing a little I think it probably migth be from an insect or just sunburn.
If it spread Ill cut te infected(?) part of the leaf. Thank you guys for the oppinions.