Connecting to European banks will be easier, as from 14 March 2019, "Account Servicing Payment Service Providers (ASPSPs) will need to make the technical specifications of their access interfaces (whether dedicated or user-facing) available to TPPs, and also provide them with a testing facility to carry out trials of the software and applications TPPs will use to offer services to their users."
https://www.europeanpaymentscouncil.eu/sites/default/files/kb/file/2018-09/API%20EG%20002-18%20v1.3%20Terms%20of%20Reference%20API%20Evaluation%20Group.pdf

https://www.europeanpaymentscouncil.eu/document-library/other/terms-reference-application-programming-interface-evaluation-group-api-eg

http://blogs.deloitte.co.uk/financialservices/2018/03/psd2-finalised-standard-on-sca-and-csc-the-wait-is-over-but-questions-remain.html