AWS app tries to fill AWS account ID every time when you are in configure page and the account ID is empty. You can try the following steps:
Open splunk_app_aws/configure page, check if "Account ID" has value.
If not, check all_account_ids.csv in "lookup" folder to see if it records your account ID.
It should record your ID, otherwise, you can check splunkd.log and saas_app_aws.log to see if any exceptions popped.
If no account ID and error has been found, you can try to add it manually. You follow steps as czhang posted.
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