You might have had a response that hasn’t go through to you: your email could work fine and the GlassWire team could have sent and even re-sent the activation email. That you got the first email suggests that the activation email was sent to your other email account.
Where I came from most reports of missing emails are due to filtering by the ISP or email host before the emails hit users’ email accounts. This can arise from an overly strict spam filter or a blocked host IP when some hosted email accounts are spamming or phishing.
So I’d recommend patience and, in the meantime, perhaps you could check your email host’s support forum to see if other users are having a similar issue. If so, then the next step could be to get your email support to see if any emails were blocked or the GlassWire email host IP was blocked on the date you received the email from GlassWire.