There could be a few reasons why you only received a 5-year warranty for your Deye inverter.

1. You may have purchased the inverter from a third-party seller that did not offer the full 10-year warranty.
2. The 10-year warranty may only apply to certain components of the inverter, such as its internal circuitry, and not to other parts like the casing or the fan.
3. The 10-year warranty may only apply if the inverter is installed by a certified professional and maintained according to the manufacturer's guidelines. If you installed the inverter yourself or did not follow the maintenance requirements, the warranty may have been invalidated.

You can check the warranty details in the owner's manual or by contacting the manufacturer directly to find out exactly why you only received a 5-year warranty for your specific inverter.