Zip Co Limited is the latest buy now pay later provider to be pummelled by investors following the sharp slide in the market value of Afterpay scrip earlier this month.The value of Zip's ASX-listed shares fell 55 cents or 12 per cent to A$3.95 on Wednesday after the company revealed that the profit margin on its receivables portfolio halved in the September quarter.In a quarterly report Zip said that cash earnings before tax and depreciation as a percentage of receivables fell to 1 per cent in the three months to the end of September compared to 2.2 per cent for the June quarter.The decline is attributable to lower income from the receivables portfolio, increased sales costs and higher operating costs.While the higher operating costs are likely to be linked to the establishment of a new funding vehicle backed by the National Australia Bank, the rise in sales expenses was partly attributable to a higher bad debt rate.Zip wrote off $4.9 million in net bad debts in the September quarter compared to $3.4 million in the previous three month period.Despite the blowout in costs, Zip posted record revenue and transaction volume in the latest period.Quarterly revenue rose 15 per cent to $31 million as the company's customer base swelled by 89,000 to 1.4 million.Managing director Larry Diamond said he was pleased to report another record quarter of growth, which he attributed partly to the addition of several large merchants to the scheme."Well known enterprise brands continue to join the platform, with BigW - part of the Woolworths Group - one of the most recent additions, and a solid pipeline of new brands looking to integrate prior to the holiday trading period," he said."We are well on our way to achieving our mission to be the first payment choice everywhere and every day."Diamond and Zip's chief operating officer Peter Gray are in line to receive special performance bonuses this year, according to the notice paper for the annual general meeting in Sydney on 29 November.Shareholders will be asked to approve bonuses to the two executives and also boost the pay of independent directors.The board is seeking approval to increase the cap on non-executive directors' fees to $1 million a year from the current limit of $600,000.