TP-Link TL-WR902AC v3 is a pocket-size dual-band (AC750) router based on MediaTek MT7628N + MT7650E.
MT7650 ac chip is not supported by OpenWrt at the moment. Therefore 5Ghz won't work.
The only way to flash OpenWrt image in TL-WR902AC v3 is to use
tftp recovery mode in U-Boot:
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