True, they sell products. But they don’t support their products
In case you want to boot from USB (there’s no SATA on the M3 – I write this again and again to warn people) with this bootloader, go buy an USB-to-UART dongle, connect it, setup a build environment, download the BSP, think about applying my fixes to be able to compile with more recent GCC and a few other improvements, run build.sh, grab kernel/boot.img, realise that this is a stinky Android BLOB, get https://github.com/vhernando/split_boot_img, have a look into the ramdisk image, get a clue what needs to be done. Repeat this a few times, lern a lot about the ARM architecture, boot loaders, kernel parameters, how crappy Allwinner’s BSP is SinoVoip still relies on instead of adopting the changes the community already made. And so on.
This will take you only a few hours/days/weeks but you will be done way earlier since indefinitely waiting for an answer from SinoVoip is the alternative
Isn’t it amazing how different everything is with devices called “Banana Pi M2/M3” compared to the “Banana Pi M1” where all this works out of the box (since the community developed all this stuff which will never happen with the M3). You bought an expensive paperweight.