As of April 1, 2020, customers could claim that their supplier issues e-invoices. While initially only applicable for B2G transactions, Finland extended the scope also to B2B transactions. Established entities (customers) can definitely claim e-invoices, it is unclear whether this also applies to non-Finnish entities.
The EU VAT Directive 2006/112/EU requires that e-invoices can only be accepted upon agreement with the customer. Any exception to this regulation requires approval from the European Commission. Finland has been creative to circumvent the approval process with the EU.
Source valtiokonttori.fi
Unofficial translation in English
Unofficial translation in English
Source Basware