Will the accountant be sinful if he makes the workers sign payment receipts at the request of his sponsor, who disregards advice and bears the responsibility?

It is not permissible to obey the sponsor in forbidden matters, such as lying to workers or oppressing them. The one who does so is sinful for assisting in wrongdoing and falls under the threat of the Hadith (definition): "Whoever helps an oppressor with falsehood to suppress a truth with his falsehood, then he has disassociated himself from the covenant of Allah and the covenant of His Messenger." The sponsor does not bear your sin, for each has his share of sin; as Allah Almighty says: "Every soul, for what it has earned, is retained."