This section covers the issues most partners run into when setting up and operating their integration — mostly around connectivity and configuration, where a small missed step can look like a bigger problem than it is. If something isn't working as expected, check here before opening a support ticket; most of these have a quick fix.
Aritma's outbound IP is 51.13.18.180.
Most likely you've missed a step in event subscription validation.
When a subscription is created or updated, the partner must complete a validation handshake before event delivery begins. Aritma's Events API runs on Azure Event Grid, which uses this handshake to verify that the webhook endpoint is authorised to receive events. If this step isn't handled correctly, subscription creation will fail with a 400 error — this is a validation issue, not a credentials or authentication problem.
How it works:
- Azure sends an
OPTIONSrequest to the partner'sdelivery.url - This request includes a
Webhook-Request-CallbackURL, delivered on port 553 (e.g.https://rp-westeurope.eventgrid.azure.net:553/...) - The partner must respond to this request to complete validation
Option 1 — Callback via port 553
The partner's server makes a GET request to the Webhook-Request-Callback URL.
- Requires: outbound port 553 open in the firewall
- Advantage: simplest to implement — follows the standard Azure flow
- Disadvantage: requires a firewall change for an uncommon outbound port. Based on experience, this single step generates the most support enquiries of anything in the events setup.
Option 2 — Response headers (no extra ports required)
Instead of calling the callback URL, the partner's server responds directly to the OPTIONS request with the following headers:
| Header | Value |
|---|---|
WebHook-Allowed-Origin | * or eventgrid.azure.net |
WebHook-Allowed-Rate | e.g. 100 (max events per minute) |
This completes validation with no outbound calls to port 553 required — recommended where firewall changes are hard to get approved.
Critical: Event delivery does not come from Aritma's IP address (
51.13.18.180). That IP is for Aritma's own outbound calls (e.g. the validationOPTIONSrequest and payment/API traffic). Actual event deliveries originate from Azure Event Grid infrastructure, so whitelisting only Aritma's IP will cause events to silently never arrive even though the subscription itself looks healthy.