Some of the new Sonoff Basics ( and probably others ) are being delivered with solder filling the serial programming interface.
So if you want to flash it,
...Show more you need to either remove the solder or you will need some dexterity to hold your 4 wires (Vcc, Gnd, RX, TX) to the proper point, depress the button, plug in your USB UART TTL adapter (3.3 volts only), release the button and flash the device. Do-able, but difficult.
That's where this clip comes in. Print it, put in pogo-pins in , connect to your USB UART TTL adapter and it will hold the pins to the right connectors.
The pogo pins I am using are P75-E2 Convex Tip Metal Spring Test Probe Pin, 1.5 mm Diameter. Link here https://www.amazon.com/gp/product/B018YPQ6ZK/
