I can see you've been trying hard to file your CT600 — you've attempted it 9 times now, most recently just before you sent this message. The frustration is completely understandable.
The issue: Every attempt has failed with the same error — HMRC is rejecting your Government Gateway credentials. This happens before TinyTax can submit your return.
Your Accounts are fine — they were accepted by Companies House on 21 January.
To fix the CT600:
The credentials you're entering don't match what HMRC expects. Please double-check:
1. Government Gateway User ID — this should be 12 characters (letters and numbers)
2. Password — make sure it's for your business Government Gateway account, not a personal one
3. Company UTR — verify this matches exactly what HMRC has on record (you can find it on letters from HMRC about Corporation Tax)
If you haven't filed a CT600 online before, you may need to enrol for Corporation Tax online first — this is a one-time HMRC setup:
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The issue: Every attempt has failed with the same error — HMRC is rejecting your Government Gateway credentials. This happens before TinyTax can submit your return.
Your Accounts are fine — they were accepted by Companies House on 21 January.
To fix the CT600:
The credentials you're entering don't match what HMRC expects. Please double-check:
1. Government Gateway User ID — this should be 12 characters (letters and numbers)
2. Password — make sure it's for your business Government Gateway account, not a personal one
3. Company UTR — verify this matches exactly what HMRC has on record (you can find it on letters from HMRC about Corporation Tax)
If you haven't filed a CT600 online before, you may need to enrol for Corporation Tax online first — this is a one-time HMRC setup:
https://www.gov.uk/guidance/enrol-your-company-for-corporation-tax-online
Once your credentials are correct, click "Update Credentials & Retry" on your dashboard and it should go through.
Your CT600 isn't due until 30 September 2026, so there's no deadline pressure — but I know it's frustrating to be stuck.
If you're still having trouble after checking these, let me know and we can look at other options.