VVProduction If your "Enable Order Invoice Email" setting is turned ON, if SendGrid Configuration is correctly set and if the Customer email is correctly set, then there is no reason for the email to not be delivered.
Kindly change the customer's email and check with a different email address. Make sure to check the "Updates", "Promotions", "Forums", "Spam" and "Inbox" all the folders on your email.
Lastly, check the SendGrid dashboard, if there is an issue of non-delivery.
If the customer's email address looks spammy to SendGrid, they might flag it and not even send the email. (exceptional)