John rents a flat from Adam for one year starting from January 2020 to December 2020. Monthly rental is $1500. Due to COVID-19 and the resulting lockdown, John is unable to pay the full rent. Adam agrees to reduce the rent by half for six months starting from February 2020. Adam sends John a notice on 01 July 2020 stating that payments should return to the original rental amount and that he wishes to collect the arrears of rent from last six months as John has got a new job now.

Can Adam insist that John should pay the arrears of rent?