Can't remove account from Organization that created by Terrraform

Hello.

If you want to close an AWS Organizations member account, you can do so by following the steps in the following document.
You can close it by performing the operation from the AWS Organizations management account.
https://docs.aws.amazon.com/organizations/latest/userguide/orgs_manage_accounts_close.html

By the way, setting up IAM Identity Center should allow you to sign in to member accounts.
https://docs.aws.amazon.com/singlesignon/latest/userguide/identity-center-and-orgs.html

When you create a member account through AWS Organizations (including via Terraform), the account may not have all the information required to operate as a standalone account, which can prevent removal. Here are steps you can take to resolve this issue:

To gain access to the member account:

1. Use the OrganizationAccountAccessRole: When an account is created through Organizations, an IAM role called "OrganizationAccountAccessRole" is automatically created with administrative permissions. You can assume this role from the management account to gain access to the member account.

2. Assume the administrator role: From your management account, use the IAM console to assume the OrganizationAccountAccessRole for the member account. This will give you administrative access without needing the root password.

3. Change the email address: If you don't have access to the email address associated with the member account, you can change it through the Organizations console to an email address you can access. Then you can reset the password.

Before removing the account, ensure it meets these requirements:

• The account must have a valid payment method
• The account must have a verified phone number
• The account must accept the AWS Customer Agreement
• The account must choose a support plan
• The account must provide and verify required contact information

If you encounter a "ConstraintViolationException" error when trying to remove the account, it typically means these prerequisites aren't met. Verify the payment method and phone number are properly configured.

If you continue to experience issues after completing these steps, particularly if there's a billing-related problem, you may need to contact AWS Support through the AWS Support Center at https://console.aws.amazon.com/support/.
Sources
Troubleshooting AWS Organizations - AWS Organizations
Remove a member account from an AWS Organization | AWS re:Post
Manage AWS organization accounts | AWS re:Post