Other than that, can you show us the Application Links page whether you have any defined apps?
If you see 0 links, you may want to contact Atlassian support - this may indicate that there is still a previously stored appLink somewhere in the backend, which was not properly cleared (at least what I came across Server->Server, I imagine Cloud could have a similar issue).
If you have another application link, then you may want to compare the Server ID of that application and your Confluence instance. Server ID must be unique in terms of application links.
On October 20, 2021, Atlassian published a security advisory for Jira Service Management. The full advisory is available at this link. We've seen a number of questions already asking for...
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