Should I pay additional money to make a corrections in GATE 2021 application form

are u sure ? that late fee wont be applicable after oct 1?

Indian Institute of Technology, Bombay has extended the date for filling the application till October 7, 2020 without any late fee. So the correction window will be opened after the registration process gets over. Most probably, by the third week of October, 2020 the correction facility may be started. However it will be notified through the official website. So keep checking the official site for furthur updates. http://engineering.careers360.com/articles/gate-application-form-correction
For modification of details such as name, gender, category, Parents details, educations details you don't have to pay any fee. But if you want to correct previously selected Exam paper and exam city, then fees are applicable. You have to pay Rs. 300 for modification in Exam paper, and Rs. 400 for changing exam centre within India. Check out the above link, all details are mentioned properly.