Hello.
At 4,400 kms the clutch belt broke.
I bought another one online and it has broken at 100 km.
I don't know if I should check something on the atv before installing the new belt?
Some help?
Thank you.

[2015 Z Force 800 53/Trail EPS]

A through inspection and cleaning for one. I see belt matks and possible damage on the primary in your photo. If there is any area of the primary that has a warn spot or flat area, its gone and will eat belts forever. The oneway also needs inspected and with those miles likely needs replaced...they don't usually last that long.

So get a straightedge and lay it across the sheaves and look for anything like this:
 

Also What belt did you put on a did you line up the balance marks ?

First of all thank you very much for helping.

I have checked the primary and secondary and I see no damage, I am attaching the photo, in case you see something.
The strap was from aliexpress, possibly of poor quality.
I don't know what "did you line up the balance marks" is. I just removed one strap and put the other on.
If you can tell me what it is and how to do it "did you line up the balance marks". And if you would check something else before installing the new belt.

Thank you so much.

[2015 Z Force 800 53/Trail EPS]

Sheaves look OK. Probably the belt quality...lol. Go with OE but they are expensive, next best is Ultimax, then Gates.

Balance marks- watch this video:

https://youtu.be/dhFR66YR4Z0