@p_vnct said in DUET 3 mini 5+ Your Duet rejected the HTTP request:
SD card 0 detected, interface speed: 0.2MBytes/sec
That's not right, the speed should be much higher. Either the SD card is bad, or there is a fault in the SD card interface circuitry of the Duet. As you have already tried a different SD card, please follow the instructions given by @Phaedrux to claim a replacement under warranty.