NR5307 5G Router latest firmware.

Hi everyone,
I recently purchased a second-hand Zyxel NR5307 5G router. It turns out to be custom-branded by the Dutch operator Odido (formerly T-Mobile Netherlands).
The router is locked to its original carrier. When I insert an Italian SIM card, the device shows no signs of life, completely failing to register on the network or connect to the internet. Additionally, trying to run an online over-the-air (OTA) upgrade fails with an information retrieval error.
Here are the system details from my web UI dashboard:
• Router Model: Zyxel NR5307
• Module SW Version: QuectelT830R03A01_xx.001.xx.001
I am looking for the generic/stock global firmware file (usually a .bin or an official ZCOM firmware image like V1.00(ACJT...) or newer) so that I can flash it manually and unbrand the
Does anyone have a working download link to the generic firmware for this specific MediaTek T830 / Quectel setup, or know how I can successfully request it? Any guidance on the manual flashing procedure would be immensely helpful.
Thank you in advance for your support!
Once you post this on the Zyxel Community Forum, let me know if you need help translating any replies you receive or if they ask you for more system information from your router dashboard!