Key Takeaways
- A C# Android SMS gateway API is HTTPS/JSON from your worker to a paired phone — not a Complete C# SDK or official NuGet package.
- Developer Center owns live fields. The C# codebase page owns copy-paste samples. This spoke owns failure modes.
- Timeouts duplicate OTP unless you send an idempotency key.
- Do not block ASP.NET request threads on the radio. Queue, then send.
- You bring the Android and operator credit. We meter devices and platform send volume.
- Free 300 lifetime / Developer 25,000 per year pause; Starter/Pro/Business uncap platform volume with device caps.
HttpClient to a SIM, not a NuGet
C# Android SMS gateway API work is a worker (or minimal API) posting HTTPS JSON so a paired Android sends on operator airtime you bought. It is the same radio path as PHP or cURL. It is not Twilio-shaped helper libraries and it is not a “complete SDK” product line.
Hub: Android SMS gateway API. Samples: C# HTTPS/JSON. Live params: Developer Center. Order-alert spoke: ASP.NET order alerts.
“If your package.json equivalent is a NuGet named SMS Gateway SDK, you invented a product we do not ship.”
{ }
JSON on the wire. Radio on the shelf.
Samples vs this in-depth
Copy-paste lives on the codebase page. This page is retries, thread pool, DLR handlers, and why a successful 202 is not a delivered SMS. DLR, webhooks.
What C# code must own
| Concern | Do | Don’t |
|---|---|---|
| Transport | HttpClient factory, TLS 1.2+ | New HttpClient per request forever |
| Auth | Keys from env/secret store | appsettings committed to git |
| Send | Idempotency key per OTP/order | Polly retry the body blindly |
| Threads | Background queue / Channel | Await radio in the MVC action |
| OTP vs bulk | Separate device pool | One hosted service for everything |
Polly without idempotency
Transient HTTP retries are correct. Duplicate SMS are not. Store the message id; treat DLR copies as the same event. Webhook practices.
Cost
Devices + platform volume. Operator pack on the SIM. Starter 2 / Professional 5 / Business 15 if you need a spare. Pricing.
Checklist
- No SDK branding in internal docs.
- Idempotency + HMAC tests.
- Worker not request-thread.
- Canary on a cold handset.
- OEM exemption on the phone.
Next steps
C# samples, setup, Android app.
Related product pages
Jump to the live product docs for this topic—not another long-form article.
- SMS API documentationLive endpoint reference
- C# REST send samplesC# code examples
- device and SMS volume pricingPlans and allowances
- Android SMS gateway product guideDefinition, product, and how to buy
