Bitmain signature lock explained (March 2024+)
Why Bitmain firmware from March 2024 blocks third-party firmware, and how the toolkit flow installs anyway.
Since March 2024 Bitmain signs its stock firmware and the bootloader refuses unsigned images. A plain web-upload of custom firmware fails with an ssh error on these builds.
The Install Toolkit 1.7.1+ handles this with a network NAND flow that works on stock of any date, with two known exceptions (Antminer L9 FR-1.19 and S19k Pro FR-1.28).
If the toolkit reports an ssh error, first apply the newest stock web-update, then retry. Unsure about the exact board revision? Ask support before any stock update. Amlogic boards from September 2025 additionally lock the USB port and need an unlock step first.