As of Jan 1, 2020, Non-resident taxpayers are obliged to register for VAT in Bulgaria at the time of their first taxable supply except supplies subject to reverse charge (currently VAT registration is only mandatory if threshold of BGN 50,000 will be exceeded)
Source: (§ 17 of the Bill for amending and supplementing the Corporate Income Tax Act 902-01-52 / 09.10.2019