However, despite the drop, its revenue for the full year increased by 15% to £22.5m.
Nektan says its Q4 fall was due to similar factors which had impacted its results in Q3, the main reason being increased UK regulation around player marketing and verifications.
The group claims it is continuing to work on expansion and growth in international markets.
Full-year B2B revenue reported significant growth compared to 2018, rising 308% to £1m for 2019.
But B2C net gaming revenue dropped from £5.1m in Q3 to £3.8m in Q4, a 26% fall, despite growing for the full year.
Lucy Buckley, Nektan CEO, said: "While Q4 saw a continuation of the B2C trading conditions we experienced in Q3, we have taken decisive action to structure the company in response to the changing gaming environment."
Despite revenue falling in H2, Buckley remains confident of a stronger financial year in 2020.
She said: "A number of steps to enhance our product offering, including the launch of bingo and improved player journeys, have been completed in Q4 and we look forward to the new financial year with optimism."
