When I open the Experience Profile tab on my Sitecore 9.1.1, I get an error: An error has occurred.
In Chrome console: Failed to load resource: the server responded with a status of 500 (Internal Server Error) --/sitecore/api/ao/v1/contacts/search?&pageSize=20&pageNumber=1&sort=visitCount%20desc&Match=*&FromDate=null&ToDate=null:1
On opening that api uri, getting '{"Message":"The requested resource does not support http method 'GET'."}'
Verified XConnect running, solr url without # and Newtonsoft.Json.dll version.
/sitecore/api/ao/..
client API require POST requests, so it is expected to receive the message that the requested endpoint doesn't support the GET method when browsing the API endpoints in your browser. I recommend to search in your application Sitecore logs for an error related to the 500 Internal Server Error that you experienced in your browser console.