BAM has been accepting electronic invoices via the Federal Government’s Central Invoice Submission Portal (CISP) since 27 November 2019. You can reach the CISP at xrechnung.bund.de.
From 27 November 2020, electronic invoicing will be mandatory. Exceptions to the obligation (for example, in the case of direct orders up to €1,000, excluding VAT) are regulated in § 3 paragraph 3 of the Federal E-Invoicing Ordinance (E-RechV).
BAM’s “Leitweg-ID” is: 991-06480-14