Genuine questions: why does this service require a login? Why does it require a secure login?
It's bad practice to not use a secure login, because anyone who is sniffing HTTP traffic can see your Uptime Robot username and password in plaintext.
This might not be that bad for this website, but keep in mind how many people use the same email/password for other services, or their email.
you should be using a password manager and have unique for every service.