"While we stand humbled by the sheer faith that such a large number of customers have shown in us, we are unhappy that we were unable to live up to the expectations of millions more who wanted to buy from us yesterday. And this is not acceptable to us," Flipkart founders Sachin Bansal and Binny Bansal said in a joint e-mail to customers.
The e-commerce firm said 1.5 million people shopped at its portal on October 6 to take benefit of the one-day sale scheme. The company claimed it sold products worth over Rs 600 crore in just 10 hours under the scheme.
They added that the load on server led to intermittent outages that impacted shopping experience on the website.
Flipkart had deployed nearly 5,000 servers and had prepared for 20 times the traffic growth - but the volume of traffic at different times of the day was much higher than this, the mail said.
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Customers have complained about getting products at different prices than it was displayed. Flipkart apologised to the price change complaints and the pricing of several products got changed to their non-discounted rates for a few hours.
"We realise that this breaks the trust our customers have put in us. We are truly sorry for this and will ensure that this never happens again," the e-mail said.
Flipkart's founders said that many of the products went out of stock within seconds the sale started.
The Bansals said they are working to ensure availability of additional units for the products that went out of stock and promised to do "level best to ensure that we minimise any cancellations".
"Everything that we have achieved at Flipkart is purely on the basis of our customer's trust and faith...We failed to live up to this promise yesterday and would like to apologise once again to every single customer for our failure," the founders said.