This is the original battery. Why is it saying it’s not an apple battery

Read this support article up to the end:--> About genuine iPhone batteries - Apple Support

For any further question/doubt, please contact Apple Support using this link:--> Get Support

Regards

Giulio

Where did you buy this device from? Please ask the store from where you bought or ask the person who sold it to you.

About genuine iPhone batteries - Apple Support (IN)

If you need to replace your iPhone battery, it's important to get a repair by certified technicians who use genuine Apple batteries. Lithium-ion ...