My B2C tenant user flow is not working anymore even when I try to test the flow through protal

Question

My B2C tenant user flow is not working anymore even when I try to test the flow through protal

Illimar Pihlamäe 20

So tenant "B2CAlphaAcedamyOU.b2clogin.com" is not resolving for me with "curl" and I am getting reports from users that they can't access the site and when I try to test out the flow in portal I am also getting an browser can't resolve the DNS and I am completely lost

if its of any important me and our users are based in Estonia, this is a bit of a side project and noone really has touched the initial setup for years and it worked yesterday ?

Rukmini 43,915 Reputation points Microsoft External Staff Moderator

2026-03-18T17:13:38.8233333+00:00

Hello Illimar Pihlamäe

Can you please test nslookup B2CAlphaAcedamyOU.b2clogin.com and share the output so that we can assist you further!
Rukmini 43,915 Reputation points Microsoft External Staff Moderator

2026-03-19T20:46:24.85+00:00

Hello Illimar Pihlamäe

Can you please test nslookup B2CAlphaAcedamyOU.b2clogin.com and share the output so that we can assist you further!

Illimar Pihlamäe 20

Hi sorry its been a bit crazy, but I am quite sure its my ISP issue now as other networks can access, but here you are

C:\Users\illim>curl -I https://b2calphaacedamyou.b2clogin.com
curl: (6) Could not resolve host: b2calphaacedamyou.b2clogin.com

C:\Users\illim>nslookup B2CAlphaAcedamyOU.b2clogin.com
Server:  PII
Address:  PII

*** ns4.starman.ee can't find B2CAlphaAcedamyOU.b2clogin.com: Non-existent domain

C:\Users\illim>

Rukmini 43,915 Reputation points Microsoft External Staff Moderator

2026-03-20T18:07:21.65+00:00
Hello Illimar Pihlamäe

Please raise a support request with your ISP and request:

DNS cache refresh / correction

Verification of resolution for:

*.b2clogin.com

1 answer

Your answer

Rukmini 43,915 Reputation points Microsoft External Staff Moderator

2026-03-18T17:13:38.8233333+00:00

Hello Illimar Pihlamäe

Can you please test nslookup B2CAlphaAcedamyOU.b2clogin.com and share the output so that we can assist you further!
Rukmini 43,915 Reputation points Microsoft External Staff Moderator

2026-03-19T20:46:24.85+00:00

Hello Illimar Pihlamäe

Can you please test nslookup B2CAlphaAcedamyOU.b2clogin.com and share the output so that we can assist you further!
Illimar Pihlamäe 20 Reputation points

2026-03-20T06:12:59.7333333+00:00

Hi sorry its been a bit crazy, but I am quite sure its my ISP issue now as other networks can access, but here you are

C:\Users\illim>curl -I https://b2calphaacedamyou.b2clogin.com curl: (6) Could not resolve host: b2calphaacedamyou.b2clogin.com C:\Users\illim>nslookup B2CAlphaAcedamyOU.b2clogin.com Server: PII Address: PII *** ns4.starman.ee can't find B2CAlphaAcedamyOU.b2clogin.com: Non-existent domain C:\Users\illim>
Rukmini 43,915 Reputation points Microsoft External Staff Moderator

2026-03-20T18:07:21.65+00:00

Hello Illimar Pihlamäe

Please raise a support request with your ISP and request:

DNS cache refresh / correction

Verification of resolution for:

*.b2clogin.com

Answer 1

The B2C login host not resolving indicates a DNS or endpoint issue in front of the B2C tenant, not a user-flow configuration problem.

Perform these checks in order:

Verify the hostname really fails in DNS
- From a machine outside the network, run a DNS lookup (for example, nslookup B2CAlphaAcedamyOU.b2clogin.com).
- If the lookup fails with an error like “host name could not be resolved in DNS,” it confirms a DNS resolution problem.
- The documented guidance for this symptom is to verify that the required DNS records exist and are correct; if not, they must be recreated or fixed in the authoritative DNS zone.
Check for custom domain / Front Door issues
- If a custom domain or Azure Front Door is used in front of B2C, misconfiguration can cause 404 or “resource not found” errors when accessing user flows.
- Confirm that:
  - Any custom domain used with B2C is still registered and successfully verified in the B2C tenant.
  - The CNAME for the custom domain still points to the correct Azure Front Door frontend host.
- If the custom domain is misconfigured or removed, testing the flow from the portal can also fail.
Validate that the B2C custom domain is not in a failed state
- If a custom domain is configured for B2C and Azure Front Door, verify:
  - The default route in Azure Front Door is enabled.
  - The custom domain verification in the B2C tenant shows as successfully verified.
- Misconfigured or disabled routes or unverified domains can cause errors when accessing user flows.
Use a generic DNS troubleshooting approach
- If DNS resolution still fails:
  - Use nslookup (or an equivalent tool) to confirm whether any A or CNAME records exist for the hostname.
  - If no records exist, the DNS host record must be recreated in the authoritative DNS zone (or the service that previously owned the name may have been removed).

If DNS for the b2clogin.com host has stopped resolving and there is no control over that DNS zone (for example, if the underlying B2C tenant or its configuration was deleted or changed), the only remediation is to restore or recreate the correct DNS/endpoint configuration or use a working B2C tenant/host name.

References: