The mini One Stop Shop came into force on 1 January 2015 and allows taxable persons supplying telecommunication services, television and radio broadcasting services and electronically supplied services to non-taxable persons in Member States in which they do not have an establishment to account for the VAT due on those supplies via a web-portal in the Member State in which they are identified.
This scheme is optional, and is a simplification measure following the change to the VAT place of supply rules, in that the supply takes place in the Member State of the customer, and not the Member State of the supplier (a derogation to this place of supply rule applies as from 1 January 2019 for supplies by certain taxable persons, whose relevant annual turnover does not exceed EUR 10,000 –). The mini One Stop Shop is available to taxable persons which are established in the EU (the Union scheme), as well as taxable persons which are not established within the EU (the non-Union scheme). Without the mini One Stop Shop, the supplier would be required to register in each Member State in which he supplies services to his customers.
In practice, under the scheme, a taxable person which is registered for the mini One Stop Shop in a Member State (the Member State of Identification) electronically submits quarterly mini One Stop Shop VAT returns detailing supplies of telecommunications, broadcasting and electronically supplied services to non-taxable persons in other Member States (the Member State(s) of consumption), along with the VAT due. These returns, along with the VAT paid, are then transmitted by the Member State of Identification to the corresponding Member States of consumption via a secure communications network. The mini One Stop Shop VAT returns are additional to the VAT returns a taxable person renders to its Member State under its domestic VAT obligations.
Find more information here: https://ec.europa.eu/taxation_customs/business/vat/telecommunications-broadcasting-electronic-services/content/guides_en