Receiving a 500 error while testing Zapier login trigger despite API functioning in Postman

Other Questions Zapier
1

I am trying to set up a webhook trigger that activates when a user logs into my system. My authentication API needs specific headers and body parameters to work correctly.

Headers:
{
    "tenant-id": "{{tenant_id}}",
    "event-id": "{{event_id}}",
    "Api-Key": "{{api_key}}",
    "Device-id": "{{device_id}}"
}

Body:
{
    "email" : "{{email}}",
    "Password": "{{pwd}}"
}

When I perform a test using Postman with these same headers and body, everything runs smoothly. However, Zapier gives me a 500 internal server error during the trigger test.

I’ve checked the headers and body parameters thoroughly, but I can’t determine the issue. Has anyone else encountered something similar? What could be the differences in how Zapier and Postman handle these requests?

2

That 500 error is probably from content-type issues or how each platform handles auth tokens. I’ve hit this exact problem - API worked perfectly in Postman but died in Zapier because they serialize JSON differently. Check if your server needs application/json content-type specifically. Zapier often defaults to application/x-www-form-urlencoded, which breaks backend parsing. Also watch out for timezone handling in timestamps or session validation that treats automated requests weird. Turn on detailed logging for your API endpoint and compare what Zapier sends vs Postman - look for differences in content encoding and any automatic parameter transformations Zapier does.

3

zapier has this default user-agent that some servers block. your backend could be set to only allow certain agents or ranges. also, make sure your api allows for webhooks and check if it needs a verification signature. those headers can trip things up!

4

I had the exact same problem when connecting to a third-party auth service through Zapier. Turned out to be case sensitivity in the headers - Zapier normalizes header names differently than Postman, and some APIs are picky about casing. Also found that Zapier adds default headers my API server didn’t expect, which broke validation on the backend. Log the actual request hitting your server when Zapier calls it - you’ll probably spot differences in header formatting or extra parameters. Also check if your API has rate limiting or IP restrictions that might handle Zapier’s servers differently than your local Postman requests.