A constellation of prominent Sydney and Auckland investors are in line to score fat returns on their seed investments in Kiwi instalment finance provider PartPay after Zip Co announced a buyout of the business on Tuesday.Zip's mostly scrip-based offer values the New Zealand buy-now-pay-later (BNPL) specialist at up to $NZ65 million.PartPay, which has a strategic partnership with New Zealand's largest retailer The Warehouse Group, has delivered more than 250,000 finance plans to 110,000 customers since it was established in January 2017.The acquisition, expected to complete at the end of October, will give Zip a platform to challenge Afterpay in New Zealand, the United States and the UK.PartPay recently set up a fully owned subsidiary in London where it is actively marketing its BNPL platform to local merchants.Zip also secures a gateway to the US market through PartPay's equity in QuadPay - one of the fastest growing BNPL players in North America.Part Pay currently owns around 4 per cent of QuadPay, but Zip will boost its stake to 15 per cent after agreeing to invest an extra US$ 11.4 million in the New York-based fintech.PartPay also opens a window for Zip in South Africa through the target company's 25 per cent interest in instalment payments provider, Payflex.Zip managing director Larry Diamond said the acquisition was first step towards putting the group on a global footing."This transaction marks the beginning of Zip's global expansion story," he said."Whilst we see significant upside in the core Australian business, we feel the timing is opportune to begin investing abroad as we seek to build a global payments business."Diamond said that PartPay's founder and largest shareholder John O'Sullivan would be joining Zip's senior management group to help oversee the company's development outside Australia.According to filings made to the NZ companies registry, O'Sullivan and members of his family control around one third of the business.He and other PartPay shareholders will receive upfront payments worth NZ$50 million in the form of new Zip Co scrip.Additional scrip-based payments of up to NZ$15 million will be distributed to shareholders over the next two years if undisclosed transaction volume targets are met.PartPay's other big shareholders include Sydney investment company Sturt Capital Partners, which controls almost 20 per cent.Sturt, which has acted as PartPay's primary adviser on the deal, is owned by a collection of former Merrill Lynch and Allco Finance Group executives.Sturt Capital directors include former Allco chief risk officer Tony Stocks.Family members of Ratesetter Australia chief executive Daniel Foggo control around 19 per cent of the company. Foggo has been a director of the PartPay board since April 2017.Other investors in line to gain from the transaction include Judo Bank directors David Fite and Greg Ruddock.Sydney investment banker Gary Stead holds a 2 per cent interest in PartPay through a private company known as Kupuna Pty Ltd.While issue of the scrip consideration to PartPay shareholders will dilute the interests of Zip's existing investors by around 5 per cent, the market response to the transaction was overwhelmingly positive.Zip's share price closed