An SOP is a statement of purpose: an essay about why you want to study a particular course at a particular place. It is a university application document. It is not a visa document, and of the United Kingdom, Australia, Canada and the United States, only Canada asks for anything resembling it.
That sentence is the whole post, and it is worth reading twice, because the amount of money changing hands in Kathmandu valley for SOP writing suggests a great many people believe the opposite.
Who asks for what
The United Kingdom asks for nothing of the kind. GOV.UK lists the documents you must provide for a Student visa, and there are two: a current passport or other valid travel documentation, and a Confirmation of Acceptance for Studies from your course provider. Everything else on the page is conditional: proof of funds, an ATAS certificate, a TB test, parental consent. A statement of purpose appears nowhere, in any form, required or optional.
Australia stopped accepting essays in 2024. For applications lodged on or after 23 March 2024 the Genuine Temporary Entrant requirement was replaced by the Genuine Student requirement, and the change was not cosmetic. Instead of an open statement, the online form contains specific questions: your current circumstances including ties to family, community, employment and your economic situation; why you want to study this course in Australia with this particular provider; how completing it will benefit you; and anything else you want to add. There is a limit of 150 words per answer, and all answers must be in English.
A two-page SOP pasted across those four boxes does not answer them. It answers a question nobody asked, in the wrong place, and it uses up the word limit doing it.
Canada is the one that genuinely wants a letter. IRCC lists a letter of explanation among the documents for a study permit and marks it recommended rather than required. What it asks you to do is narrow: explain why you want to study in Canada, and show that you understand your responsibilities as an international student. That is closer to a covering letter than to an essay about your dreams.
The United States decides at the interview. There is no document upload where a statement would go. The case is made by a person, out loud, in a few minutes, and what you would have written in an SOP you instead have to be able to say.
Why the confusion is so profitable
Every student applying abroad does write a statement of purpose at some point, because universities ask for one. That part is real. The slip is in what happens next: the document gets filed with the visa paperwork, an agent notices it there and starts charging to write it, and within a few years an optional university essay has been rebranded as a visa requirement in a market where nobody has read the government list.
The test is simple and you can run it yourself in about four minutes. Open the government page for your destination, the three linked at the foot of this post being the primary sources, and search it for the phrase. If it is not there, it is not required.
What to write instead, per country
For a university application, write the statement the university asks for, at the length the university sets, about the course and what you intend to do after it.
For Australia, answer the four questions in the form, separately, inside 150 words each, and make each answer land on something you can evidence. The Department states that it gives more weight to claims supported by evidence. "My uncle's business will employ me on my return" is worth writing only if the business registration is in the file.
For Canada, write a short letter of explanation covering the two things IRCC names, and nothing else.
For the United Kingdom, write nothing for the visa. Spend that time on the 28-day bank balance, which is what actually refuses UK applications.
For the United States, practise saying it.
The part that transfers
There is one real skill underneath all of this, and it is not writing. It is being able to explain, in your own words and without rehearsal, why this course, why this country, and what happens afterwards. Australia asks it in four boxes, Canada in a letter, America across a counter, and a university in an essay. The answer has to be the same answer every time, because the file is read as a whole and an SOP that disagrees with the rest of it is worse than no SOP at all.
If you cannot give that answer yet, no amount of paying somebody else to write it will fix the application. It will only make the gap harder to see until somebody at a desk finds it.