Get Invoice Endpoint

Taxpayer ID (txpay_…). Required with an organization API key (pk_…) for this taxpayer-specific operation, even for one taxpayer. Not a TIN. Optional with a taxpayer access token, which already names its taxpayer.

Grant ID (tgr_…) to act through, with an organization API key. The request then has exactly that grant's scopes and fails once the grant is revoked. Without it, the key acts through all of the organization's active grants on the taxpayer.