Hello and welcome to Community Central. Since your account was crated about 3 hours 30 minutes ago (relative to this reply; 8 minutes ago relative to your reply), I assume you are new. Here on Community Central, we ask that users please do not reply to old inactive threads (i.e. any thread where the last reply is at least a month or two ago) unless there is critical information to add or you are the person who started the thread.
One of the reasons for this is that Fandom is always changing things. Whether it be bug fixes or major changes to the software, the status and nature of various features change over time. Therefore, even if issues appear similar, they may not be if too much time has passed. In this particular case, the thread is discussing a feature that no longer exists. Starting on March 11, 2020 and ending in January 2021, Fandom moved all of its wikis to a newer version of the core software and the feature discussed in this thread was removed.
The error you are talking about is related to Feeds, the replacement for the feature discussed here. The two features, although serving similar purposes, work entirely differently and almost no issues with the new feature would be relevant to the old one. That said, I will quickly address your issue.
Here are the 3 most-common causes of the issue you are experiencing. On the wiki you are trying to post on:
Currently, there is a 4th reason impacting users globally. Fandom has implemented a supposedly temporary restriction which requires users to confirm their emails in order to get permission to post. That said, as of my reply, it looks like you have already done that.
Edit: If you need more help resolving your issue, please start a new thread instead of replying here.