While it is best practice to whitelist the Mobilize.io domain as a whole we understand that due to some firewall settings that might not always be possible. In the instances where this cannot be accomplished you can also whitelist our IP range provided by Amazon AWS. That range is: 

{
      "ip_prefix": "13.34.66.0/27",
      "region": "us-east-1",
      "service": "AMAZON",
      "network_border_group": "us-east-1"
}

This is current as of September 14, 2023 but is subject to change. The most updated list of ranges can be found on the AWS Ip-Ranges site: 
https://ip-ranges.amazonaws.com/ip-ranges.json

Please contact support if you find you are having troubles after whitelisting this range or the domain.