Remove the duct tape, cardboard and insulation and repair it right. Get some sheet metal or aluminum, pop rivet it in place, cover seams with foil tape, then cover all of the patch with mastic duct sealant.
Make sure all of duct is sealed and all of belly is sealed.
IF all of duct is done and burner and burner orifice is clear, time to call an hvac tech.
Some people are Humbly Grateful, while some are Grumbly Hateful.................... Which one are you ?