I haven’t run into this one for a few months, but the first time I saw it, it really aggravated me.
Canary? Invalid? Invalid Canary?
I would really like to see an error that is meaningful and helpful, and this one is far from either.
Anyway, the cause of the error, each time that I have seen it, is the URL for ECP. If you happen to run into this error, it is probably the ECP’s URL. Each time, I have seen that it is either a mixed case or upper case issue. For example, https://email.companyname.com/ECP or https://email.companyname.com/Ecp can be fixed by changing the URL to https://email.companyname.com/ecp.