Hi there,
So I see this allot , seems it works if you use the GPIO Number in place of the Pin name or physical pin number.
for example: To use the A0 or D0 pin in your code, You address it as GPIO2.
If your using some serial LIB in there, then GPIO21, GPIO20 would be used for TXD(D6) and RXD(D7).
Talk about cheap, No user LED, C’mon Seeed …
so that too would be by the GPIO Number it is assigned too.
HTH
GL 
PJ 
See here,