Package delivery firm Postmates raised $16 million in Series B funding today. The latest round will help the San Francisco-based startup improve its mobile app, according to The Register.

Investors who led and contributed to the funding were not disclosed, the report added.

Founded in 2011, Postmates' system is similar to that of its contemporaries including Uber, Taskrabbit, and Lyft. The delivery service operates a mobile app and a team of contractors who use different vehicles to delivery stuff on demand. The company offers a one-hour delivery of packages within the San Francisco area, the report detailed.

Feedback from workers, however, shows that the couriers themselves are not happy with the compensation they receive, the report stated.

A Postmates spokesman released a statement to The Register: "Our platform is home to thousands of happy service providers in the delivery space, offering great customer service every day. While we can't comment on anonymous reviews, we're happy to share that the service providers receive 75 per cent of the delivery fee and 100 per cent of tips earned. Service providers are required to keep a minimum customer satisfaction rating on the Postmates platform at all times."