Not sure if I am the only having this problem: Failed to parse server response

I am setting up authentik new and I have created 3 apps portainer, Synology DSM and Proxmox all using OIDC. Everything works fine with Portainer but

Proxmox returns the error 401 unauthorized. Logs show this:
`Jan 06 23:47:04 proxmox-host pvedaemon[2449387]: openid authentication failure; rhost=::ffff:10.0.0.62 msg=Failed to contact token endpoint: Failed to parse server response`

I reviewed Synology logs as well but they don't help either:
`User [] from [10.10.10.11] failed to sign in to [DSM] via [sso] due to authorization failure.`

In authentik logs it says application authorized.

When I send curl request to /application/o/token/ with client id and key I get proper response.

I am using Let's Encrypt certificate for web so it is secure connection.

Not sure what else I can check.