We use following IPs in our cron job executing bots:
198.27.83.222 (IPv6: 2607:5300:60:24de::)
198.27.81.205 (IPv6: 2607:5300:60:22cd::)
198.27.81.189 (IPv6: 2607:5300:60:22bd::)
192.99.36.110 (IPv6: 2607:5300:60:4b6e::)

Please make sure our IPs can reach your cron job scripts/programs.
Our bots will use IPv4 unless the destination server forces us to use IPv6.
A JSON format IP list could be found at https://www.easycron.com/ips.json.