Building a telco, in public.
Technical guides from the engineers building Firsty.
How to provision your first eSIM via API in 30 minutes
From OAuth token to first eSIM activated, with QR code generation server-side. Real code, real credentials, real eSIM, in about 30 minutes.
OAuth2 client credentials in production: what most tutorials get wrong
Token caching, refresh strategy, and the security mistakes we see in production integrations every week.
How Pexx built a white-label travel eSIM product on top of the Firsty API
A case study on how the cryptowallet Pexx integrated the Firsty API to launch loyalty-driven free data for their users in under three months.
The LPA activation code format explained
What the LPA format actually is, how to render QR codes from it correctly, and why some QR codes work on iPhone but not Android.
Why two-step eSIM provisioning beats single-call APIs
Bundled provisioning APIs feel simpler. They are worse in production. Here is why separating eSIM creation from package ordering matters.
Bulk-provisioning 1,000 eSIMs without hitting rate limits
Exponential backoff, idempotency keys, and how to design a queue that survives partial failures.
Building a travel eSIM marketplace: schema, pricing, activation flow
A complete blueprint for building a travel eSIM business: database schema, pricing strategy, activation UX, and what to skip in v1.
profileReference vs esimReference vs ICCID: which identifier when?
Three identifiers, three meanings, frequently confused. Here is which one to use where.