Welcome to the fun of upgrading older GL iNet routers.
You may have to step up to firmware to 4.3.17. Start with the 3.105 firmware, then do an online upgrade the 3.216 firmware using the tar file, and then do the online upgrade to 4.3.17 firmware using the tar file.
If you have an old AR300m, then your Uboot code may be too old to load 4.x using Uboot. You can upgrade your Uboot code, BUT be very careful, as if you load the wrong file, your router is permanently bricked, and becomes e-waste
Look at this page, and make sure you expand the Upgrade the Uboot Version section:
New Uboot code is at:
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All that said, on my AR300m routers, I am running either the GL iNet 3.216 firmware or the or the generic OpenWrt 23.05.x firmware for the GL-AR300M NAND, as both these versions of the firmware just work. I tried 4.3.x, and did not feel it was finished. Currently, I am unhappy with the lack of support on 4.x for the older GL iNet routers as the newer routers are getting new features in 4.6.x, that are missing in 4.3.x. 