Hi @rhino007US,
In terraform console I evaluated the following expression:
cidrsubnet("10.0.0.0/16", 2, 2)
This produced the result I expected: 10.0.128.0/18.
This suggests to me that the issue in your case is that aws_vpc.environment-example-two.cidr_block is different than you expected. In the terraform plan output, can you see what value Terraform is reporting for cidr_block inside the resource "aws_vpc" "environment-example-two" block?
The other strange thing about the behavior you are seeing is that you said you are passing a network number of 2, but you reported that the result was 10.0.0.0/24. Even if that had the expected prefix length, 10.0.0.0/18, that is still incorrect because it includes network number zero rather than network number 2.
Unfortunately I can’t offer any further ideas without seeing some real examples from your configuration to see how things are connected. It seems like something unusual is happening here but I can’t tell what that is from the information you’ve shared so far.