What are your plans for the final project?

Top row SimConnects Inputs has no limit except minimum time between inputs. Do a complete turn of a rotary encoder rapidly and the Link2fs monitor will show every string coming in but there may be some strings missing going to the board. I suspect that this originates in FSX and the last string is always passed on to the Arduino. Do a frequency swap and FSX may ignore another command for up to 60 milliseconds.

Uploading commands to Link2fs is software generated. Depending on the situation one pin can trigger one of several different SimConnect Inputs. The number of pins is always a factor, but you can use input/output expanders or simple shift registers to expand input and output capabilities. Then available ROM and RAM becomes a factor. Keep a margin of 200 to 500 bytes above what Arduino says is available.

EXPERT? Not me. There could be more information available. I suggest installing Link2fs experts in a second folder for development and testing. An error in one line will disable anything that follows, so use this version to test one command in the top line and transfer the code to your working version when successful. Type over the last test line with your next line to test.

SimConnects was an ongoing project when MS FSX folded. Some instructions were not developed and the documentation was not always updated. Dropping "KEYS_" from the big black text for SimConnects inputs should work to do something but try the text in the next box or try short forms of the longer words. Search the web to see if others have found the solution.

FSUIPC is ongoing and and they do great work with a small team. Payware publishers may or may not release the custom offsets for their aircraft.

Always keep in mind that FSX began as a game and thankfully as MS developed the graphics for the game, they through in something for the pilots.