Thanks for posting your question here.
Although eBay did return the API warning message you are referring to when you attempted to post this listing, the warning does not actually account for the failure to post. In order to determine why the listing failed, just click the red number in the “Notifications” section along the top of your account.
Based on the error message that was returned, it appears that eBay does not support the “Good til Canceled” duration for the category you selected, so you should just have to select a different duration (or category) in order to post this item successfully.
I will also bring this to the attention to our technical team, so we can update our system to no longer show this invalid duration for this category with a future update to our site.
I hope this clears things up. If you need any further assistance with this, please feel free to contact our Customer Support team directly from under the “Help” tab on our site and we will be happy to continue working with you on this.