The comma shouldn't be there, because it's not legal .json format. But I tried it with and without it, and I couldn't find any difference, jetways were visible in both cases, but we fixed the file online anyway.
Now, VISIBLE GSX jetways only means the package has been activated in the sim correctly, but whether they work or not, is a completely different matter. If you see the "bad jetway data" error, it means GSX GOT a "bad jetway data" error from Simconnect, the reasons might be multiple:
This is different depending if you use MSFS 2024 or MSFS 2020:
If you are using MSFS 2020
- The only thing to check is to be sure if you are using a 3rd party or handcrafted default airport, GSX replacement jetways have been DISABLED for that airport, since they are only meant to be used for bare default airports.
- If GSX replacement jetways have been DISABLED for that airport, your problem IS NOT GSX, if the jetway doesn't work, it's completely unrelated to GSX.
If you are using MSFS 2024
- GSX replacement jetways are not even INSTALLED in MSFS 2024 so, again, your problem IS NOT GSX, if the jetway doesn't work, it's completely unrelated to GSX.
If you are using MSFS 2024 or you are using MSFS 2020 and you still got the "bad jetway data" error, the problem might be a conflict caused by another scenery. If you have Navigraph Navdata installed, try without it.