Hi
Please refer to guidance on GOV.UK at Pay your Corporation Tax bill: Overview.
The 17 digit Corporation Tax payment reference is on your 'notice to deliver your tax return' or any reminders from HMRC.
It is also on the company's HMRC online account:
- choose view Corporation Tax statement,
- accounting periods,
- then select the correct period.
Please note, the reference changes with each accounting period and payment may be delayed if you use the wrong one.
Thank you