I don’t think that’s exactly what happened 
There was no ready-to-use document with all the process steps that could be followed.
This situation has not changed imho, but let’s try to change it.
Update or Not Update Android
I started installing Sailfish as soon as I took the device out of the box. According to the information I received from lokenk, he first applied the updates available on the Android side and then started installing Sailfish and had a smoother experience.
Decide if and how much to update Android. You can get help by asking questions on this topic in the forum.
Developer Developer Developer - Steve Ballmer
Enable developer mode and unlock the bootloader in the settings. Since this is not enough, also use unisoc-unlock or another tool to unloock bootloader:
adb reboot bootloader
python3 -m unisoc_unlock unlock
The Road Not Taken - Robert Frost
It seems that there are three primary ways to install Sailfish.
one
Use original tools from the chipset manufacturer and system firmwares that may be provided by Reeder.
This was not an option for me as Reeder did not provide me with the necessary files even though I asked them.
two
You can follow the instructions in Fastboot flashing of Jolla C2 with minor modifications.
sudo fastboot flash boot_a hybris-boot.img
sudo fastboot flash boot_b hybris-boot.img
sudo fastboot flash uboot_a lk.bin
sudo fastboot flash uboot_b lk.bin
sudo fastboot flash vendor_boot_a vendor_boot.img
sudo fastboot flash vendor_boot_b vendor_boot.img
sudo fastboot flash dtbo_a dtbo.img
sudo fastboot flash dtbo_b dtbo.img
sudo fastboot flash userdata sailfish.img001
sudo fastboot flash super fimage.img001
sudo fastboot reboot
three forro - İbrahim Tatlıses
You can follow affe_null’s newly prepared document Flashing the Jolla C2 using the Unisoc flash mode.
Find the appropriate icon2img for the operating system you are using.
https://www.google.com/search?q=simg2img
Get the most up-to-date or suitable Sailfish OS image from Index of /images/ and extract it into a directory named SailfishOS. Then run these commands to flash them:
simg2img SailfishOS/sailfish.img001 sailfish.img
simg2img SailfishOS/fimage.img001 fimage.img
./spd_dump \
exec_addr 0x65015f08 \
fdl fdl1-dl.bin 0x65000800 \
fdl fdl2-dl.bin 0x9efffe00 exec \
w uboot_a SailfishOS/lk.bin \
w uboot_b SailfishOS/lk.bin \
reset
# Hold down the volume up key while the phone reboots!
./spd_dump \
exec_addr 0x65015f08 \
fdl fdl1-dl.bin 0x65000800 \
fdl SailfishOS/lk.bin 0x9efffe00 exec \
w boot_a SailfishOS/hybris-boot.img \
w boot_b SailfishOS/hybris-boot.img \
w vendor_boot_a SailfishOS/vendor_boot.img \
w vendor_boot_b SailfishOS/vendor_boot.img \
w dtbo_a SailfishOS/dtbo.img \
w dtbo_b SailfishOS/dtbo.img \
w userdata sailfish.img \
w super fimage.img \
reset
Please feel free to provide additional information so that users of all levels can follow the document more easily
Thanks again to everyone.