The on-board debugger is connected to the ATtiny3217 by default. These connections must be removed before any external microcontroller can be programmed or debugged. Cut the GPIO straps shown in the figure below with a sharp tool to disconnect the ATtiny3217 from the on-board debugger.
Figure 1. Programming and Debugging
Connections to Debugger
Info: Cutting
the connections to the debugger will disable programming, debugging, and data streaming
from the ATtiny3217 mounted on the board.
Tip: Solder in 0Ω resistors
across the footprints or short-circuit them with solder to reconnect the signals between
the on-board debugger and the ATtiny3217.