OSS Invoices (One-Stop Shop Scheme)

In this case, in addition to using vatKey = 17 and causeExemption = 2, the Base must be sent calculated without applying taxes, and the same applies to the Total invoice amount.

See section 3.28 — When is key 17 used (“Operation under any of the regimes in Chapter XI, Title IX — OSS and IOSS”)? in the
SII Frequently Asked Questions.