HMRC Admin 8 Response

I work from home as a freelance journalist in the UK but for, among other clients, a France-based company. They asked for a certificate of residence to prove I pay tax in the UK. There are several form questions that are unclear to me: 1. Which article of the country's Double Taxation Agreement covers the income in this request? There are two: Articles 23 and 24. But the form only permits one! Can I just enter one? No idea which is more pertinent. 2. Do the subject to tax provisions apply to this foreign income? (Some Double Taxation Agreements state that a UK resident is only entitled to foreign tax relief on certain types of income if it is subject to tax in the UK). I’m guessing I should tick ‘yes’, as I will be paying tax on the income to HMRC? 3. Have you worked outside the UK? AND How many days did you spend outside the UK? Despite working from home ordinarily I spent three days working (as a journalist) at a conference in Paris. So I tick 'Yes' and 3 days? 4. Are you requesting a certificate in advance? (This is before you have spent 183 days in the UK during the tax year of your arrival or departure). This is a bizarre sentence, but since we are fewer than 183 days into the tax year in which I spent 3 days in Paris, do I click ‘Yes’? 5. Ticking ‘Yes’ to the question above then prompts: "Are you arriving in or leaving the UK?" Er…. Neither? This was in the past? Sorry for so many questions… Thanks in advance.