Which IP ranges are used by AWS Elastic Beanstalk in ap-southeast-2 (Sydney)?

third-party provider (ePages)...
list of IP ranges that Elastic Beanstalk might use in this region to handle traffic from our application.

To confirm, are you asking about the IP address used by EB EC2 instances to connect to public internet?

I assume your EC2 instances are in a VPC private subnet. If yes, outgoing internet connectivity is through NAT Gateway which has a fixed IP as it uses Elastic IP.

You can provide this IP to the provider.

Hello.

AWS publishes its public IP address ranges in "ip-ranges.json".
Among them, the IP address of "ap-southeast-2" is currently as follows.
Therefore, it is thought that it will be used by ElasticBeanstalk from the following range.
Please note that "ip-ranges.json" is updated regularly.
By the way, for outbound communication from Elastic Beanstalk, it is possible to fix the public IP address using a NAT Gateway.
https://docs.aws.amazon.com/vpc/latest/userguide/aws-ip-ranges.html

curl "https://ip-ranges.amazonaws.com/ip-ranges.json" | jq -r '.prefixes [] | select (.region=="ap-southeast-2") | select (.service=="AMAZON") | .ip_prefix' | sort

1.178.11.0/24
103.8.172.0/22
104.255.59.87/32
104.255.59.88/32
13.146.0.0/16
13.210.0.0/15
13.236.0.0/14
13.239.245.0/24
13.248.102.0/24
13.248.109.0/24
13.54.0.0/15
136.18.23.0/24
15.134.0.0/16
15.134.66.0/23
15.135.0.0/16
15.177.83.0/24
15.193.164.0/22
15.193.3.0/24
15.221.128.0/22
15.221.20.0/22
15.230.107.0/32
15.230.107.2/31
15.230.115.0/24
15.230.149.0/31
15.230.149.10/32
15.230.149.11/32
15.230.149.2/31
15.230.149.4/31
15.230.149.8/31
15.230.210.0/23
15.230.212.0/23
15.230.22.0/24
15.230.222.0/24
15.230.23.0/24
15.230.78.128/26
15.230.78.192/26
15.230.78.64/26
15.251.0.8/32
15.251.0.9/32
150.222.112.0/24
150.222.119.0/24
150.222.142.0/24
150.222.43.128/27
150.222.43.64/27
150.222.43.96/27
150.222.44.192/26
150.222.47.0/26
150.222.47.64/26
150.222.72.0/24
150.222.82.0/24
150.247.37.0/24
151.148.39.0/24
16.12.74.0/24
16.176.0.0/16
16.176.35.128/25
16.176.69.0/25
16.177.0.0/16
16.178.0.0/15
173.83.212.0/24
18.98.192.0/19
3.104.0.0/14
3.104.82.0/23
3.2.77.0/24
3.24.0.0/14
3.24.227.192/26
3.25.138.0/26
3.25.138.64/26
3.25.178.128/26
3.25.37.64/26
3.26.137.0/24
3.26.140.64/26
3.27.176.0/22
3.4.12.1/32
3.4.12.15/32
3.4.12.16/32
3.4.12.17/32
3.4.12.18/32
3.4.12.2/32
3.4.13.0/28
3.4.13.16/28
3.4.15.16/29
3.4.15.24/29
3.44.64.0/18
3.5.164.0/22
3.5.168.0/23
32.236.0.0/15
35.55.10.0/24
35.55.11.0/24
35.55.12.0/24
35.71.97.0/24
35.96.128.0/20
35.96.240.0/24
35.96.39.0/24
40.238.0.0/16
40.239.0.0/16
43.220.0.0/16
43.221.0.0/16
43.249.44.0/24
52.119.210.0/23
52.144.224.64/26
52.144.228.64/26
52.144.229.0/26
52.62.0.0/15
52.64.0.0/17
52.64.128.0/17
52.65.0.0/16
52.93.126.130/32
52.93.126.131/32
52.93.126.136/32
52.93.126.137/32
52.93.126.138/32
52.93.126.139/32
52.93.182.128/26
52.93.32.183/32
52.93.33.10/32
52.93.33.11/32
52.93.33.224/32
52.93.33.225/32
52.93.33.230/32
52.93.33.231/32
52.93.33.8/32
52.93.33.9/32
52.93.77.0/24
52.93.78.0/24
52.94.13.0/24
52.94.152.176/32
52.94.152.177/32
52.94.152.178/32
52.94.152.179/32
52.94.152.180/32
52.94.152.181/32
52.94.152.182/32
52.94.152.183/32
52.94.198.112/28
52.94.248.64/28
52.95.128.0/21
52.95.241.0/24
52.95.255.16/28
52.95.36.0/22
54.153.128.0/17
54.206.0.0/16
54.239.0.112/28
54.240.192.0/22
54.240.203.0/24
54.240.204.0/22
54.252.0.0/16
54.253.0.0/16
54.66.0.0/16
54.79.0.0/16
64.252.106.0/24
64.252.107.0/24
64.252.108.0/24
64.252.109.0/24
69.107.9.208/29
69.107.9.216/29
96.0.0.0/21
96.0.184.0/22
96.0.72.0/21
96.0.8.0/22
96.0.80.0/22
99.150.32.0/21
99.77.144.0/24
99.77.239.0/24
99.78.170.0/23
99.78.212.0/22
99.82.184.0/22
99.83.120.0/22
99.83.80.0/22