# Help: ICP Gateway returns Error 400 Unknown Domain

**URL:** <https://forum.dfinity.org/t/help-icp-gateway-returns-error-400-unknown-domain/56948>\
**Category:** Developers\
**Created:** [September 7, 2025, 1:57pm UTC](https://forum.dfinity.org/t/help-icp-gateway-returns-error-400-unknown-domain/56948 "2025-09-07T13:57:33Z")\
**Posts on this page:** 1\
**Showing post:** 24

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**Author:** ![barolukluk](https://avatars.discourse-cdn.com/v4/letter/b/3d9bf3/32.png) [@barolukluk](https://forum.dfinity.org/u/barolukluk)\
**Post date:** [October 11, 2025, 12:21pm UTC](https://forum.dfinity.org/t/help-icp-gateway-returns-error-400-unknown-domain/56948/24 "2025-10-11T12:21:02Z")

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I’m experiencing the same issue with my apex domain `mimento.ai`.

- The domain was working fine before — then suddenly stopped issuing a valid certificate.

- `www.mimento.ai` continues to work without any problems.

- For the apex domain, the status now loops between `PendingAcmeApproval` and `Failed: order is unable to reach 'Ready' status`.

- All CAA, TXT, and `_acme-challenge` CNAME records are correct and DNS resolves properly.

- I also deleted the previous registration request and created a new one, but the problem persists.

As a temporary workaround, I enabled Cloudflare **proxy for the apex CNAME record** and set up a redirect from `mimento.ai` → `www.mimento.ai`.

This avoids the certificate error, but it’s not a real fix.  
Is there a known issue on the DFINITY side regarding ACME for apex domains, or any way to manually reset the challenge?

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