ONDC /subscribe api domain verification file(ondc-site-verification.html) is not found

Question

I am currently working on ONDC integration with our app. We are onboarding as seller app. I am following this given repo. I am completed till step 5 where I have to generate the ondc-site-verification.html file and expose it on our server. And after that I am hitting "https://staging.registry.ondc.org/subscribe" on postman with proper request body as mentioned in documentation, but I am getting the API response as:

{
    "message": {
        "ack": {
            "status": "NACK"
        }
    },
    "error": {
        "type": "DOMAIN-ERROR",
        "code": "130",
        "path": null,
        "message": "<https://example.com> : Domain verification file (ondc-site-verification.html) is not found "
    }
}

I have checked my server and the "https://example.com/ondc-site-verification.html" is working properly as mentioned in documentation. But still ONDC staging subscribe is still unable to find the verification file.

Can anyone please help me out with this?

Note : I have tried checking on the similar task to take reference and resolve the issue like "google-ste-verification" but in my case it seems like "/subscribe" API is unable to find the ondc-site-verification.html from my server. I have tried to mention tag like "ONDC", "Signature-Verification" etc. But because of my low reputation I'm unable to do so. Please let me know if there is anything more needed from my side.