Hi there @cchcny,
Welcome to the Community! 
Before we dive deeper into this, it seems like the subreddit you're attempting to post to requires a flair to be added before making a post. I noticed that there is no "Flair" field or any way to include a flair when using the "New Link Post" action.
To troubleshoot, could you please try skipping the action step by clicking on "Skip test"? After that, give the Zap another go and see if the error persists.
Please keep us posted! 
Hi @ken.a I did as you suggested and skipped the test and published. But even after the Zap ran, Reddit did not post (other platforms in the zap ran successfully), likely because of this missing Flair.
I hope Zapier will look into this?
Hi @cchcny,
Thanks for trying that out!
This could be a good feature request for the “New Link Post” action. I recommend reaching out to our Support team. They can create a feature request on your behalf. You can contact our Support team by visiting this link: https://zapier.com/app/get-help. Once there, choose the "Report a bug or request a feature" option. They'll be more than happy to assist you and forward your request.

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Hopefully, this helps! 
This essential feature for 90% of subreddits not available 11 months later 
Thanks for reaching out here @guyinroom. Really sorry that the feature request hasn’t been implemented yet. I can see that you also contacted our Support team and they added your vote to the feature request, which will help to increase it’s priority. While I can’t make any promises as to when you can expect the feature request to be implemented, we’ll be sure to email you when/if it is!
As a workaround, you might want to try using Reddit’s API Request (Beta) action to add a flair. It’s a bit more advanced as you’d need to reference Reddit’s API documentation to set up the request (see: https://www.reddit.com/dev/api#POST_api_flair), but we have a general guide on working with API Request actions that you might find helpful: Set up an API request action.
Hope that helps, If you run into any issues with that workaround do let us know - happy to assist further! 
Edit: @cchcny - I just double-checked the feature request and you’re vote wasn’t on it so I’ve added your vote for it as well so we can notify you if it’s added. 
Hey folks, just popping back in with a quick update to share that the feature request has finally been implemented! 
Thank you all so much for your patience on this, it really is appreciated.
The Create Post action now includes a dynamic flair dropdown, that will allow you to select a flair.
If you give it a try and run into any issues please open a new topic in the Community, or reach out to our Support team for further assistance.
In the meantime, happy Zapping! 