In Safaricom Daraja sandbox runs from September 18–23, 2026, I found that a repeated AccountReference did not prevent two accepted STK Push submissions, query error 500.001.1001 did not reliably mean a reference was unknown, and failed callbacks were not redelivered during the periods I observed. These are bounded observations—not guarantees about production or Daraja 3.0.
I ran the tests with shortcode 174379, test MSISDN 254708374149, and amount 1. The sandbox payer never answered the prompt, so I did not observe a successful payment or its callback. Safaricom describes M-Pesa Express as the prompt API for Buy Goods or Pay Bill payments; the official Daraja developer portal describes Daraja 3.0 as its platform for Safaricom and M-PESA APIs. My results below apply only to the setup and dates stated here.
1. The STK Push password is encoded, not hashed
The request password is formed as base64(BusinessShortCode + Passkey + Timestamp). Base64 is reversible encoding, not encryption or hashing. In practical terms, a captured request body can expose the passkey material used to construct that value.
Treat STK Push request bodies as secret-bearing data: avoid logging them, and redact them before they reach application logs, tracing systems, or support exports. This is a security implication of the described request format; it does not establish Safaricom’s current credential rotation or revocation procedures.
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2. A query error did not tell me whether a reference existed
In my sandbox queries, error 500.001.1001 appeared for an unknown reference and also for a reference that I knew existed. For the known reference, four of nineteen queries returned HTTP 500 with that error; other queries seconds apart returned HTTP 200.
For this observed setup, treat that response as an unknown status rather than proof that no transaction exists. Preserve a pending or indeterminate state and query again according to your reconciliation process; do not turn this one sandbox result into a universal Safaricom error contract.
3. Reusing AccountReference did not stop duplicate submissions
I submitted two requests with the same AccountReference. Both were accepted and received different CheckoutRequestID and MerchantRequestID values. In these tests, the reference was not an idempotency key.
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Make duplicate protection an application responsibility before calling Daraja. Associate a unique merchant-side operation or order with a single initiation attempt, and handle a repeated client action against that record instead of blindly submitting another payment request. This observation does not rule out other Safaricom mechanisms that were not tested.
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4. The immediate response omitted AccountReference
The initiation response I observed included MerchantRequestID, CheckoutRequestID, ResponseCode, ResponseDescription, and CustomerMessage, but not the caller’s AccountReference.
Persist the relationship between your order or payment attempt and the Safaricom request identifiers when you submit the request. Do not depend on the immediate response to return your own reference for later matching.
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5. One CheckoutRequestID looked like Nairobi local time
One identifier was ws_CO_180920261803512708374149. My recorder associated it with 15:03 UTC; the apparent embedded time, 18:03:51, is three hours ahead, consistent with UTC+3.
That is one sample, not evidence of a stable encoding contract. Treat CheckoutRequestID as an opaque identifier; do not parse its apparent date or time to establish when a transaction occurred.
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In the request example I examined, BusinessShortCode was a JSON number, while Amount and PartyB were strings. PartyB and BusinessShortCode carried the same value, but not the same JSON type.
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Match the documented field types rather than assuming that equal numeric meaning makes a number and a string interchangeable. The example alone does not establish whether sending a different type causes a request to be rejected.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.7. I did not observe callback redelivery after two delivery failures
After I returned HTTP 500 from the callback receiver, I saw no further delivery for 31 minutes. When the receiver was unreachable, I saw no further delivery for 44 minutes. Those are observation windows in my sandbox run, not proof that delivery can never be retried under other conditions.
Safaricom’s integration document says failed callbacks are not repeated and directs integrators to confirm a request through Transaction Status Query or the M-PESA organization portal when callback delivery fails. The practical design implication is to build a reconciliation path rather than depend solely on callback delivery.
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8. ResultCode was more consistent than ResultDesc in my observations
Code 1037 appeared across several observations while the accompanying description text varied. I also saw code 4999 once with a description indicating that processing was still underway.
In this limited sandbox report, the code was a more consistent branching signal than the prose description. Use code-based handling for the cases you have explicitly mapped, and preserve an unknown or pending path for values you have not mapped. These observations are not an exhaustive result-code specification.
Quick Recap
What these tests cannot establish
- Successful payment behavior: the sandbox payer never answered the prompt. I have never seen a successful payment in these runs, so the successful callback metadata, receipt number, and payer-MSISDN shape are not established here. Any modeled simulator success path is not an observed payment.
- Production behavior: no production shortcode was tested, so these results should not be used as production guarantees.
- Daraja 3.0 behavior: I have not rechecked these observations against Daraja 3.0.
- Full error coverage: other result codes and the behavior for unknown codes remain outside these observations.
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