HMRC letter codes · One-to-many letters
CI357MMLetter about income from online marketplace sales
Published by its source on 18 January 2023. A date in the letter that has passed stays passed: what a passed date means.
Last reviewed 14 October 2026 · How Tax Letters checks its facts
In short
HMRC's letter CI357MM is headed “Income you have earned from Online Marketplace sales”.
“CI357MM … Income you have earned from Online Marketplace sales”
ICAEW: HMRC letter CI357MM, as published with its tax news item · checked 14 October 2026
Information, not advice: this page reports what HMRC, GOV.UK and the bodies named publish about CI357MM. Each fact has its source and the day it was checked beside it.
When HMRC sends it
ICAEW said, in the news item with HMRC's letter CI357MM, that letters were being sent out from the week commencing 16 January that invite recipients to correct their tax affairs, where necessary, by making a digital disclosure.
“Letters are being sent out to taxpayers from the week commencing 16 January that invite recipients to correct their tax affairs, where necessary, by making a digital disclosure.”
ICAEW: HMRC campaign targets income from online marketplaces and digital content · checked 14 October 2026
HMRC's letter CI357MM says HMRC has information that the reader earned income from Online Marketplace sales and has not told HMRC about some or all of it, which means the reader may owe tax.
“We have information that shows you’ve earned money (income) from Online Marketplace sales. We also have information that shows that you have not told us about some or all of this income. This means you may owe tax.”
ICAEW: HMRC letter CI357MM, as published with its tax news item · checked 14 October 2026
What it asks
HMRC's letter CI357MM asks the reader to fill in the enclosed certificate of tax position and send it back.
“Please fill in the enclosed certificate of tax position and send it back to us”
ICAEW: HMRC letter CI357MM, as published with its tax news item · checked 14 October 2026
How to send it or apply
HMRC's letter CI357MM says a reader with income to tell HMRC about can do so by making a voluntary disclosure using HMRC's online Digital Disclosure Facility.
“If you have income you need to tell us about You can tell us now by making a voluntary disclosure using our online Digital Disclosure Facility.”
ICAEW: HMRC letter CI357MM, as published with its tax news item · checked 14 October 2026
Free help and HMRC contacts
HMRC's letter CI357MM says a reader who needs help can contact HMRC using the details at the top of the letter, and points to GOV.UK, search “get help from HMRC if you need extra support”.
“If you need help, please contact us using the details at the top of this letter. … For more information, go to GOV.UK and search for ‘get help from HMRC if you need extra support’.”
ICAEW: HMRC letter CI357MM, as published with its tax news item · checked 14 October 2026
Free help first
These routes are described by GOV.UK, TaxAid and Citizens Advice themselves.
- HMRC's extra supportHMRC offers extra support if your health condition or personal circumstances make it difficult to contact HMRC, for example a mental health condition, financial hardship or being treated in hospital.
- Someone to deal with HMRC for youYou can authorise a friend, relative or voluntary organisation to talk to HMRC for you and help you fill in forms.
- TaxAidTaxAid helps people with tax problems who cannot pay for advice. Tax Help for Older People merged with TaxAid in July 2025.
- Citizens AdviceCitizens Advice gives confidential advice online, over the phone and in person, for free.
- ICAEW: HMRC letter CI357MM, as published with its tax news item (checked 14 Oct 2026)
- ICAEW: HMRC campaign targets income from online marketplaces and digital content (checked 14 Oct 2026)
- GOV.UK: Get help from HMRC if you need extra support (checked 7 Oct 2026)
- GOV.UK: Appoint someone to deal with HMRC on your behalf (checked 7 Oct 2026)
- TaxAid: About us (checked 8 Oct 2026)
- Citizens Advice: About us (checked 7 Oct 2026)