Paypal INP responce FileContent "invalid"

i am receiving the pay-pal Ipn response filecontent "invalid" suddenly . I have implement the further proceeding on the base of "Varified " and now it is return "Invalid" for me.How and what what i have to do . payment proceeding successfully in my account.  there is some really harmful for me if I proceed further functionality and ignore this Invalid status ? i have no Idea about this. please suggest me better way for deal this issue. Thanks In advance