During the three months ended February 29, 2020, the Company issued 498,418 warrants to those note holders who returned interest checks and accepted payment in kind of units consisting of convertible notes with a face value of $124,603 together with 4,000 warrants for every $1,000 of accrued interest to satisfy $124,603 of accrued interest that was payable on October 31, 2019. The warrants are each exercisable for one share of common stock at an exercise price of $0.25 per share on or before the 3.8-year anniversary of the issuance. The Company also issued 150,000 warrants as payment to a consultant for marketing services. The warrants are each exercisable for one share of common stock at an exercise price of $0.25 per share on or before the five-year anniversary of the issuance.

On September 16, 2019, the Company entered into a securities purchase agreement with two investors to sell a total of 818.0 units, for aggregate principal of $818,000, at a price of $1,000 per unit, consisting of (i) $1,000 10% interest secured convertible promissory note, convertible into the Company's common stock at a conversion price of $0.15 per share and (ii) four thousand warrants each exercisable for one share of common stock at an exercise price of $0.25 per share on or before January 22, 2024. The Company issued 3,272,000 warrants in connection with this transaction. The relative grant date fair value of these warrants was estimated at $363,846 using the Binomial lattice option pricing model and reflected in additional paid-in capital.

On April 22, 2019 and May 20, 2019, the Company entered into a securities purchase agreement with several accredited investors to sell a total of 2,080.265 units, for aggregate principal of $2,080,265, at a price of $1,000 per unit, consisting of (i) $1,000 10% interest secured convertible promissory note, convertible into the Company's common stock at a conversion price of $0.15 per share and (ii) four thousand warrants each exercisable for one share of common stock at an exercise price of $0.25 per share on or before October 22, 2023. The Company issued 8,321,058 warrants in connection with this transaction. The relative grant date fair value of these warrants was estimated at $888,444 using the Binomial lattice option pricing model and is reflected in additional paid-in capital.

On October 22, 2018, the Company entered into a securities purchase agreement with several accredited investors to sell 1,275.0 units, for aggregate principal of $1,275,000, at a price of $1,000 per unit, consisting of (i) $1,000 10% interest convertible promissory note ("the 2018 Notes"), convertible into the Company's common stock at a conversion price of $0.15 per share, and (ii) four thousand warrants each exercisable for one share of common stock at an exercise price of $0.25 per share on or before the five-year anniversary of the issuance. Pursuant to this private placement, the Company issued 5,100,000 warrants. The grant date fair value of these warrants was estimated at $524,089 using the Binomial lattice option pricing model and reflected in additional paid-in capital.

The following table summarizes warrant activity during the three months ended February 29, 2020: