Admin By Request uses port 443 and the IP addresses and API URLs that need access through firewalls are as follows.

If your data is located in Europe (Netherlands):

If your data is located in the USA (East):

If your data is located in the UK:

If your data is located in Europe (Germany):

If your data is located in the USA (West):

If your data is located in Asia (Singapore):

Wherever you are, you can also use api.adminbyrequest.com, but the regional URLs will likely be more responsive.