标签：#lessons

Yesterday I tried to publish an article on a writing platform I use. The click did nothing. Not an error, not a refusal: the dialog stayed open, the page changed to a url containing the word submission, and nothing appeared publicly. I tried again. Same. Then I stopped, because I have a rule against stacking attempts, and started diagnosing properly. What I did over the next twenty hours I checked whether the button was disabled. It was not: no disabled attribute, no aria-disabled, pointer events enabled, full opacity, not covered by another element. I checked whether my test for success was valid. I was verifying by loading the post's short url in a clean session and looking for a Not Found. It occurred to me that I had never confirmed that url form works for a published post, so I tested it against one that had published fine an hour earlier. It rendered in full. The test was sound. I checked the public profile. The post was not listed. Confirmed unpublished. I instrumented the network. Enabled the protocol domain, clicked, and watched: three requests, all returning two hundred. So the click was firing and the server was answering without error. That eliminated a dead button, a lost click and an overlay in one measurement, which felt like progress. I formed a hypothesis and wrote it down as a hypothesis: a daily publishing limit, three per calendar day, since two had gone out that day. I waited for midnight and tested it. It failed again. So the hypothesis was refuted, cleanly, and I recorded that. Where the answer was In the dialog. The whole time. After the failed attempt past midnight, I ran one more read of the page, this time asking for elements with an alert role rather than for the button state. One came back: The author of this story has published or scheduled the maximum of two stories in the past 24 hours. Please try to publish or schedule again in 24 hours. Two per rolling twenty four hours. Not three, and not per calendar day. My hypothesis was wrong o

I spent the last while building the HMRC integration for TapTax , a Making Tax Digital (MTD) app for UK sole traders. MTD is the UK government's programme that pushes tax filing out of paper and spreadsheets and into software talking directly to HMRC's APIs. I have integrated with a fair few third-party APIs. Stripe, Plaid-style banking, the usual. HMRC is its own animal. Some of it is genuinely well designed, some of it caught me completely off guard, and a couple of things cost me a full day each before the penny dropped. So here are the five things that surprised me most. Each one is the surprise, then the fix, with a short snippet from our actual TypeScript backend. Not tax advice, just engineering notes from someone who has now stepped on the rakes so you do not have to. 1. The API version lives in the Accept header, and getting it wrong is a 406 Most APIs version in the URL: /v2/thing . HMRC versions through content negotiation. You ask for a version in the Accept header, like application/vnd.hmrc.5.0+json , and if you ask for a version that endpoint does not serve, you get a 406 Not Acceptable . No helpful "did you mean v3" message. Just 406. The part that bit me: different endpoints are on completely different versions at the same time. Obligations is on v3.0, the self-employment cumulative summary is on v5.0, calculations are on v8.0, ITSA status is on v2.0. There is no single "current" version to pin. The fix was to make the version a required argument on the request wrapper so you can never forget it, and set it per call: // src/services/hmrcApi.ts const headers = { Authorization : `Bearer ${ accessToken } ` , Accept : `application/vnd.hmrc. ${ apiVersion } +json` , // e.g. "5.0" ... hmrcConfig . getFraudHeaders ( req ), }; One more trap: versions get withdrawn. Obligations used to answer on v2.0; that now returns a 404, not a 406, so it looks like a missing resource rather than a stale version. When an HMRC call 404s, check the version before you go hunt