A biller processor computing system is associated with a biller. The biller processor computing system includes a processing resource, a memory resource, and computer-executable instructions stored thereon and embodied in a biller processor application programming interface (API) engine. The instructions, when executed by the processing resource, cause the biller processor computing system to extract a payer identifier from an electronic bill (e.g., an electronic bill received from the biller). Based at least on the payer identifier, a corresponding electronic token is retrieved from data storage media. The electronic token relates to payer authentication information for a biller computing system, which is communicatively coupled to the biller processor computing system. The electronic token is included in the electronic bill, and the electronic bill is transmitted to a payer computing system.