Unlike the V-series, Sunmi P-series (financial/payment) devices are strictly locked to the Sunmi App Store for security and cannot install third-party APKs.
However, the irony is that while the hardware is open, the software ecosystem is often a walled garden. These devices are usually sold to businesses (delivery fleets, restaurants) that want to lock the device down to a single app. When you try to "free" it by installing random APKs, you run into the Android kiosk mode wall. sunmi v2 install apk free
If you receive an error saying the install is blocked: Unlike the V-series