Sidecar, one of Uber's rivals, has shut down
The company has raised $35 million (£23 million) since 2012, from investors that included Avalon Ventures and Union Square Ventures.
Paul described a "significant capital disadvantage" when compared to Uber, which has raised $6.6 billion (£4.4 billion), and Lyft, which has raised $1.3 billion (£876 million).
According to GeekWire, Sidecar was the first service to introduce carpooling - which Uber now has - and stayed away from surge pricing, the controversial feature that increases the fare during busy periods.
Sidecar was also one of the first ridesharing companies to cater to businesses, offering its API to help anyone deliver good and services. The company said in August that it had the largest business-to-business network in the US, totalling 200,000 deliveries.