> As of 2025, there were 41 members in SEPA,[2][3] consisting of the 27 member states of the European Union, the four member states of the European Free Trade Association (Iceland, Liechtenstein, Norway and Switzerland), the United Kingdom, as well as five EU candidate countries.[4][5][3] Some microstates participate in the technical schemes: Andorra,[6] Monaco, San Marino, and Vatican City.[4] As of 2025, Albania, Moldova, Montenegro, North Macedonia and Serbia are the five countries negotiating to join the EU that are included in SEPA.[2]

- https://en.wikipedia.org/wiki/Single_Euro_Payments_Area

I don't know if I'd call that a "unified economic zone" without some qualifications.

Few of SEPA members have autonomous regions which are them selves not members of SEPA, I do wonder if making transactions between the autonomous region and the rest of the country, as well as to a different SEPA member is any harder. For example I can’t imagine it would be difficult to make a transaction between Thorshavn in the Faroe Islands and Hirtshals in Denmark proper, or to Oslo or Reykjavík for that matter. But a transaction between North Nicosia to Nicosia in Northern Cyprus and Cyprus respectively may be a different matter.

Here's a fun timeline to walk through how it developed and why it's been, while not trivial, implemented with a kind of structural uniformity to keep the problem space contained.

https://www.europeanpaymentscouncil.eu/about-sepa/sepa-timel...