Understanding and monitoring the space environment is of great importance for the design and development of space avionics. This is especially critical when employing radiation-sensitive commercial-off-the-shelf (COTS) components in space systems. This work presents the design, validation, and characterization of the SpaceRadMon-NG radiation monitoring payload and its sensors, a modular system built around such components. The study covers the payload configuration and preparations for the radiation effects during the in orbit flight experiment (RADIOX) mission, part of the SYNDEO-1 CubeSat. Unique methodologies were applied for radiation qualification, system-level validation and sensor characterization to ensure reliable operation in space. The payload features enhanced capabilities compared to the previous version, including improved resolution, power efficiency, and system modularity. Mechanical and radiation tests confirmed system robustness, and a cross-section smaller than 8.58ċ 10-12 cm2 was determined at a 95% confidence level. Sensor performance was excellent, with relative errors of 0.65% for the COTS static random access memory and 0.41% for the floating gate dosimeter (FGDOS) compared to reference devices. A novel FGDOS characterization under simultaneous temperature cycling and irradiation confirmed the stability of its temperature coefficient and identified an effective compensation method using a radiation-insensitive reference sensor. This compensation approach can be extended to other radiation-sensitive components in space. With its successful validation in space-representative environments, the payload is ready for in-orbit demonstration, where it will measure the total ionizing dose and high energy hadron fluence in low Earth orbit.