These are the IPs to whitelist to receiving web-hooks from Unit21. Web application firewalls should be configured accordingly.
To make sure the webhooks deliver, configure your firewall to allow the following production and sandbox IPs:
US Prod1
54.244.124.116
44.229.224.175
44.241.189.223
US Prod2
3.211.26.166
35.173.197.34
3.218.86.132
EU Prod1
3.67.166.222
3.65.10.32
52.28.10.157
US Sandbox1
52.35.88.232
44.231.188.163
35.155.45.198
US Sandbox2
34.212.4.113
44.233.196.196
44.233.237.79
EU Sandbox1
3.76.88.250
3.122.27.184
3.73.223.182