Anil, income certificate is necessary if you are planning to claim any reiumbursements. The FAQs section at: http://www.cee-kerala.org/docs/keam2020/examdetails/faq.pdf says that except for SC/ST Candidates, it's better for all Candidates to submit an Income certificate. It might help you if you want to apply for scholarships, concessions which might be announced by the Government subsequently. Because there might not be another chance to upload or submit the income certificate, it is better if you upload it now.