The 2023 fiscal year has been opened in the integration environment of the IRPF WS:

https://ws.ia.aeat.es/wlpl/iniinvoc/es.aeat.dit.adu.suap.irpfws.IRPFXMLI3SOAP

Updated documentation with the new message schemes can be found at:

Specifications of the web service for obtaining a taxpayer's IRPF certificate

For the tests, the holder's NIF must be used: 99999357A.