Get account interest details.

Account identification. The token identifies the account—the path alone is not enough. Exactly one of x-account-id or x-external-account-id must be passed and must match the {accountId} path parameter. Otherwise the request is rejected (403 on a mismatch or when neither header is passed, 400 when both are).

Identifier validation. The ID encoded in the token is confirmed to exist by calling an external API before the interest account is read:

• x-account-id: An Accounts API call confirms the account ID exists. If it does not, the request fails with 400 and account_id not found.
• x-external-account-id: A Corporate API call resolves the external account ID to a Pismo account_id. If the external account ID does not exist, the request fails with 400 and external_account_id not found.

A 404 means the identifier is valid but the account has no interest configuration. Any other failure of those APIs fails with 500.