ING: Anonymous dialog not supported without product registration number

[MichaR2112]

Problem

ING Germany (BLZ 50010517, URL https://fints.ing.de/fints/) blocks the anonymous dialog
required to fetch TAN modes, even before login:

9800 (global): Der Dialog wurde abgebrochen.

9400 (global): Der anonyme Dialog wird nicht unterstützt.

This happens regardless of the productRegistrationNumber value (tested with known open-source
IDs like 2DC4F960C86A9B39E9C5 and others).

Root cause

ING requires a server-side validated product registration number issued by Deutsche
Kreditwirtschaft (hbci-zka.de). Unknown or unregistered IDs are rejected at the BPD fetch stage.

Suggestion

Document this ING-specific requirement clearly in the README or add a specific error message
that explains registration is required, rather than a generic "anonymous dialog not supported" error.

Environment

• php-fints: 4.1.0
• PHP: 8.4
• Bank: ING Germany

[Philipp91]

The requirement for registration is not specific to ING and is documented in literally the first sentence of the "Getting started" documentation: https://github.com/nemiah/phpFinTS#getting-started

[Philipp91]

#327 (comment)