In a circular issued by the Federal Ministry of Finance on February 24, 2016 (2016/0174885), it is stipulated that the wage tax guidelines (LStR; R 8.1 Abs. 7 Nr.4) apply to digital or electronic meal vouchers, and the employer must apply the corresponding conditions. It also describes that a review of the receipts for eligibility is to be carried out. It is up to the employer whether they manually review the receipts to be reimbursed or delegate the review to the provider (e.g., Hrmony).
Additional information can be found here.