How do you flash? By bootloader / System Recovery or by STB Settings?
Firstly try flashing Infomir public image. Download it from soft.infomir.com -> choose your STB -> release -> choose version (there is only one) -> imageupdate. Follow please my guide how to do later:
https://firmware.magboxes.xyz/docs/fwflash (instead transitional image mentioned in guide use your downloaded image).
If it still refuses to flash, consider unlocking STB by serial connection. Read firstly about it there:
https://firmware.magboxes.xyz/docs/modify/unlock-mag-255/ and then let me know if it will be needed so I'll arrange some info for you :)