Thanks for your help.

The LED D1 issue is resolvable because I tried spare LED that came with the kit with temporary connections and it worked fine. When I solder the good LED onto the board, this issue will get resolved.

Regarding. button b1, I don’t yet know what is going on. With power on, the voltage at hole PC1 is about 4.3V but voltage any of four connections at b1 (button not pressed) is 0. Is b1 getting somehow grounded or connection fron PC1 to b1 is bad ? (BTW, I cannot see this connection on the back of the PCB, front connections are now hiding under components)

Comparing this to button b0 (which works), the voltage is 4.3V at two of its connections when not pressed and goes to 0 when pressed. That sounds like correct behaviour.

I have checked solders on the back of b1, they look ok (not too much or too little solder)

What can I do to resolve issue with button b1 ?

Thanks.