The situation was likely made worse by the banning of credit card charge fees. When the price incentive to pay by debit card was removed, this would also have affected cash flow driving this into the hands of the card acquirers rather than directly into the business. This wasn't the cause of Flybe's demise but just another nail being added...
With the obligations on credit card companies to refund customers who don't receive their product/flight in the event that the business fails, understandably the credit card debt acquirers want to protect themselves. For those businesses in a financially strong position that present less risk, cash is released early to provide the business with working capital, but for those struggling it was just another problem to try and overcome. When Flybe entered Administration, I think the card acquirers had about £50m held back starving Flybe of working capital.
The downside is that Flybe is no more, however the upside is that many customers will reclaim their money from their credit card companies and not be out of pocket as a result of Flybe ceasing operations.