After rebooting the firewall, we are able to obtain the certificate successfully! This must be done through the CLI when using version 7.0.3. The issue is supposed to be fixed in a later version. For anyone who has the same issue here is the commands you need to run:
config vpn certificate local
edit "certificate_name"
set enroll-protocol acme2
set acme-domain "certificate_domain"
set acme-email "email_address"
set acme-ca-url https://acme-v02.api.letsencrypt.org/directory
next