Troubleshooting the error “Error processing AuthnRequest. Could not find Single Sign-on Service URL”

I am working with a partner for implementing SAML federation. IDP has in-house federation solution and SP has fedlet. metadata is exchanged between both parties. While testing the SP initiated SSO URL, we are getting 400 error in browser as shown below. Upon looking into the logs, it throws the below exception: ERROR: Error sending […]