Azure APIM Developer portal access - Unable to start portal

Question

Azure APIM Developer portal access - Unable to start portal

Eddie Vincent 205

Issue: The developer portal itself can be logged into but displays the same as the link here "Unable to start portal" https://techcommunity.microsoft.com/blog/azurepaasblog/azure-api-management-developer-portal-troubleshooting/2790963 although you can browse API's, it doesn't pull anything down like can be seen on the introductory page here: https://free.blessedness.top/en-us/azure/api-management/developer-portal-overview#do-i-need-to-enable-additional-vnet-connectivity-for-the-new-managed-portal-dependencies

User's image

I have worked through the fixes in the outlined page above without success and at the developer tools within the browser itself it look to be trying to pull various jpg and png files but resulting with 404 (not found).

The APIM instance itself is the developer SKU (which I can find nothing to suggest SKU's would affect this), VNET injected and being accessed on the local IP (resolved DNS), user access is via Entra/Azure AD (enabled in the settings) CORS enabled and backend reachable, I have also previewed the new UI design.

Another point also - is the above expected out of the box behaviour (bar the error and lack of pulled down images) as most Microsoft pages seem to suggest otherwise.

Thanks,

Rupesh Asati 780 Reputation points Microsoft External Staff Moderator

2025-10-23T15:57:05.71+00:00
Hello Eddie Vincent,

Thanks for reaching out on Microsoft Q&A and really appreciate your patience while we looked into this.

Understand from description that you're running into some frustrating issues with the Azure API Management developer portal. The "Unable to start portal" error can stem from a few different connectivity or configuration issues, especially since you're accessing it via an internal VNET.

Please help me with below information to investigate further and also provide some information in private message.

Are you accessing the portal from within the same network that's connected to the VNET?

Can you provide details about the DNS setup for your management endpoint?

Have you made any recent changes or updates to your APIM settings?

Are any specific browser errors showing up in the console besides the 404 errors?

Thanks
Eddie Vincent 205 Reputation points

2025-10-23T16:07:07.3833333+00:00
Hi @Rupesh Asati

Thanks for the quick response - to answer your points.

I have tried from within the network in Azure, however are connected via private connectivity in most cases.

DNS is configured within the environment via AD however have tried also with amending the local hosts file on the accessing endpoint as a test, both with the same results.

No but will be in the future (unrelated to this issue).

If you take the link of the 404 and paste it directly (not via the browser tools) I get "the page your looking for doesn't exist".

I hope this adds some clarity - I read also that some of this access required needs the "Administrator" account (which I assume is the one via the Identity section in APIM) but cant see how to access in this way either.

Appreciate any feedback you may have based on the above - thanks!
Pashikanti Kumar 1,080 Reputation points Microsoft External Staff Moderator

2025-10-23T18:46:24.7066667+00:00
Hi Eddie Vincent,

Access Method and Network Dependencies

Accessing APIM Developer Portal via private connectivity (VNET integration, VPN, ExpressRoute, or peered VNET) is correct for internal mode deployments, but all relevant resources (portal, management API, media, etc.) must be resolvable and routable within that network

Deploy Azure API Management instance to internal VNet | Microsoft Learn

DNS and Endpoint Troubleshooting

Even with hosts file changes, some developer portal features (like media/image downloads) require backend resources (e.g., Azure Storage) and additional DNS/NSG configuration. These might be missed with hosts-only overrides. Use “nslookup” or “dig” to verify that all required domains resolve internally.

Issue with deploying Azure API Management instance to a virtual network - internal mode - Stack Overflow

Are there any custom DNS or firewall rules that could be interfering with outbound traffic to Azure-required services or to the internet in general?

Reference

Deploy Azure API Management instance to internal VNet | Microsoft Learn

Issue with deploying Azure API Management instance to a virtual network - internal mode - Stack Overflow

I hope the provided answer is helpful,

Please "Up Vote" if the information helped you. This will help us and others in the community as well.

Thank you.

Your answer

Rupesh Asati 780 Reputation points Microsoft External Staff Moderator

2025-10-23T15:57:05.71+00:00

Hello Eddie Vincent,

Thanks for reaching out on Microsoft Q&A and really appreciate your patience while we looked into this.

Understand from description that you're running into some frustrating issues with the Azure API Management developer portal. The "Unable to start portal" error can stem from a few different connectivity or configuration issues, especially since you're accessing it via an internal VNET.

Please help me with below information to investigate further and also provide some information in private message.

Are you accessing the portal from within the same network that's connected to the VNET?

Can you provide details about the DNS setup for your management endpoint?

Have you made any recent changes or updates to your APIM settings?

Are any specific browser errors showing up in the console besides the 404 errors?

Thanks
Eddie Vincent 205 Reputation points

2025-10-23T16:07:07.3833333+00:00

Hi @Rupesh Asati

Thanks for the quick response - to answer your points.

I have tried from within the network in Azure, however are connected via private connectivity in most cases.

DNS is configured within the environment via AD however have tried also with amending the local hosts file on the accessing endpoint as a test, both with the same results.

No but will be in the future (unrelated to this issue).

If you take the link of the 404 and paste it directly (not via the browser tools) I get "the page your looking for doesn't exist".

I hope this adds some clarity - I read also that some of this access required needs the "Administrator" account (which I assume is the one via the Identity section in APIM) but cant see how to access in this way either.

Appreciate any feedback you may have based on the above - thanks!
Pashikanti Kumar 1,080 Reputation points Microsoft External Staff Moderator

2025-10-23T18:46:24.7066667+00:00

Hi Eddie Vincent,

Access Method and Network Dependencies

Accessing APIM Developer Portal via private connectivity (VNET integration, VPN, ExpressRoute, or peered VNET) is correct for internal mode deployments, but all relevant resources (portal, management API, media, etc.) must be resolvable and routable within that network

Deploy Azure API Management instance to internal VNet | Microsoft Learn

DNS and Endpoint Troubleshooting

Even with hosts file changes, some developer portal features (like media/image downloads) require backend resources (e.g., Azure Storage) and additional DNS/NSG configuration. These might be missed with hosts-only overrides. Use “nslookup” or “dig” to verify that all required domains resolve internally.

Issue with deploying Azure API Management instance to a virtual network - internal mode - Stack Overflow

Are there any custom DNS or firewall rules that could be interfering with outbound traffic to Azure-required services or to the internet in general?

Reference

Deploy Azure API Management instance to internal VNet | Microsoft Learn

Issue with deploying Azure API Management instance to a virtual network - internal mode - Stack Overflow

I hope the provided answer is helpful,

Please "Up Vote" if the information helped you. This will help us and others in the community as well.

Thank you.

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Azure APIM Developer portal access - Unable to start portal

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