The green shoe refers to the overage provision option that the underwriters have in this case it is 15% or $2,625,000. See excerpt of the news release below.

"In addition, the company has granted the underwriters an option, exercisable within 30 days after the closing of the offering, to purchase from the company for resale up to an additional 15 per cent of the subscription receipts at the issue price for additional gross proceeds of up to $2,625,000."