Organization <ID> could not be found when try to Create resource share

The error you're encountering when trying to create a resource share as the root user, stating "Organization <ID> could not be found," is likely related to an issue with the integration between AWS Resource Access Manager (RAM) and AWS Organizations.

This problem typically occurs when the service-linked role 'AWSServiceRoleForResourceAccessManager' wasn't successfully created when you turned on the integration between AWS RAM and AWS Organizations. Even though you're using the root user, this role is necessary for the proper functioning of resource sharing within your organization.

To resolve this issue, you need to follow these steps:

1. Sign in to the AWS Management Console using your root user credentials or an IAM user with administrative permissions.

2. Navigate to the AWS Organizations console and go to the Services page.

3. Find and select RAM (Resource Access Manager).

4. Choose "Disable trusted access" for RAM.

5. After disabling, go to the AWS RAM console and access the Settings page.

6. Look for the option "Enable sharing with AWS Organizations" and select it.

7. Save the settings.

This process will disable and then re-enable the integration between AWS RAM and AWS Organizations, which should create the necessary service-linked role and resolve the "Organization not found" error.

It's important to note that while you mentioned AWS IAM Identity Center (formerly AWS Single Sign-On) is the only service enabled in your organization, this process shouldn't affect its functionality. However, be aware that temporarily disabling trusted access for RAM might briefly impact any existing resource shares within your organization.

If you continue to experience issues after following these steps, you may need to contact AWS Support for further assistance, as there could be underlying issues with your AWS Organizations setup.
Sources
Error: "Your account ID does not exist in an AWS organization" - AWS Resource Access Manager
Errors when trying to share with accounts outside of my organization - AWS Resource Access Manager