Kobomatrix generating error 500

My form is being rejected by the system after inserting begin_kobomatrix method.
I am getting error 500.
Kobo Questionaire.xlsx (51.4 KB)
If I remove this section the form gets uploaded. Tried placing the section in places inside the form with no success.
Could you please help?

Welcome to the community, @Godinho! You should be able to learn more about designing matrix question through this support article Question Matrix Response Type.