HTTP Monitor

Hello, from response output it's very clear that GET method is not allowed. You don't want to use GET method in your monitor, and checking for any string in the response you posted makes no sense since it's not a working page.

 Try using "-X POST" syntax in your curl, and look for a string in your response that will always be displayed in a working scenario. 

Then, refer https://support.f5.com/csp/article/K2167 to configure appropriate send and receive string.