The problem was that I didn´t took the right firmware. With the firmware suggested by [rajkosto] commented [on Nov 2, 2022] (.bin file inside this archive https://files.sshnuke.net/t16mod_fwupgrsignaes.7z) it didn´t work (in contrast to all other instructions by him, which worked like a charm in regard to this issue). The firmware which worked for me was [zxhnh288a_hv11_fv110_gr51t16_firmware.bin]Nova [zxhnh288a_hv11_fv110_gr51t16_firmware.bin](https://github.com/MariosK239/Gr_ISP_Router_Firmware/blob/main/Nova/ZTE_ZXHN_H288A/zxhnh288a_hv11_fv110_gr51t16_firmware.bin), posted by [datio](https://github.com/datio) on Oct 20, 2022](https://github.com/mkst/zte-config-utility/issues/43#issuecomment-1286159848).
Originally posted by @gramc1106 in https://github.com/mkst/zte-config-utility/issues/75#issuecomment-1648543450