I resolved the issue by myself.
Fastly was (correctly) sending a HTTPS request to GoDaddy.
GoDaddy doesn't support any default https certificate (i.e. Let's Encrypt) until you buy a new SSL cert.
So Fastly was not able to establish a secure connection with GoDaddy.
I just fixed by buying a SSL cert because i cannot migrate my domain right now.
But for future domains i will use another domain register that provide at least a default SSL cert.