The domain seistech.nz has an SSL certificate through Let's Encrypt, whose certificates have expiry dates, and need to be renewed.
To generate certificate (or renew)
sudo ~ec2-user/py3env/bin/certbot certonly --dns-route53 --expand --agree-tos --text --non-interactive -d seistech.nz -d *.seistech.nz
Or simply
sudo ~ec2-user/py3env/bin/certbot renew
Make sure the correct certificate is used in /etc/nginx/nginx.conf. Restart the Nginx service
sudo service nginx restart
This assumes the AWS credentials are correctly installed at /root/.aws
Consult this page for details : https://boto3.amazonaws.com/v1/documentation/api/latest/guide/configuration.html#best-practices-for-configuring-credentials