First, we enabled sharing within our AWS Organization. This can be done from the AWS RAM console, as we saw in this recipe, or by using this AWS CLI command: aws ram enable-sharing-with-aws-organization. If we do not enable sharing within our AWS Organization, the accounts we add will be considered external accounts, even if they are part of our Organization, and this may result in an error similar to the following screenshot:

We added a resource share for a subnet and shared it with another account within our OU. We added the account ID 380701114427 directly from the console. In our case, we could select the account from the organizational structure itself, but I wanted to show what is possible. We selected the option to allow external accounts. In our particular case, that was also not needed.