Hello, friend!
HG531S V1 is an ISP product. The reason is that you do not have a purchase contract signed with Huawei. The ISP resells the HG531S to you. Therefore, your application is rejected.
If you need firmware for the device, the normal program:
You convey the firmware requirements to the ISP, and the ISP applies for and downloads the firmware version using the account that purchases the contract rights, and then forwards the firmware to you.
Thanks!