They can not type in a code, and need a bar code. If you don't transfer the actual card to the buyer, he can not use it. You can try with a picture, which works in theory, but not necessarily in reality.
Why not use a barcode generator?
Selling 1x $400 @ 94.5%, QP or Venmo.
Selling ~$1300 in BB GC, all firsthand.5x$2005x$501x$55
@ what %?
selling one $400 gc at 94% physical gc