issue with external api service provided request.

The 403 Forbidden error you are encountering when using the external API service could be due to several reasons, especially since you mentioned that it works fine on a VM running IIS. Here are some troubleshooting steps you can consider:

1. IP Filtering: Ensure that the external API service does not have IP filtering rules that might be blocking requests from your Azure App Service. Even though you have whitelisted the IPs, double-check that the correct IPs are being used and that there are no additional restrictions.
2. Access Restrictions: Check if there are any access restriction policies implemented in your Azure environment that might prevent the App Service from making outbound calls to the API. This can include settings in the Application Gateway or any firewall rules.
3. Request Headers: Sometimes, the headers sent by the App Service may differ from those sent by the IIS server. Ensure that the request headers (like User-Agent, Content-Type, etc.) are consistent between the two environments.
4. Rate Limiting: Verify if the external API has any rate limiting in place that might be causing the 403 error after a certain number of requests.
5. Debugging Logs: Utilize logging features in Azure to capture detailed logs of the requests made from the App Service. This can help identify if there are any specific errors or issues in the request being sent.

If the issue persists after checking these aspects, consider reaching out to the external API provider for further assistance, as they may have more insight into why requests from your Azure App Service are being rejected.

References:

• Request throttling problems and HTTP 403 - Forbidden issues
• Error code: 403

Hi @Shanmugam Tummuru

From your description, you are trying to generate a WEBGUID using the external API endpoint https://revpay.ebs-rcm.com/BankPay/interface/WEBGUID with the provided client ID and client key. When calling this API from Azure App Service, you are receiving a 403 Forbidden error, but the same configuration works correctly when deployed on a VM running IIS. You also mentioned that both the Application Gateway IP and the App Service IP have been whitelisted by the external provider.

This behavior usually indicates that the external service is still not seeing the correct outbound IP from your App Service. Azure App Service does not use a single static outbound IP; instead, it can use any outbound IP address assigned to the App Service plan. If all of these IP addresses are not whitelisted, the external API provider may block the request, which results in a 403 error.

As a suggestion you need to whitelist all outbound IP addresses of your Web App. You can find them by navigating to: App Service → Overview → Outbound IP Addresses

Official Microsoft documentation for reference:

Feel free to post back if you need any further assistance.