Amendment a capital gains real time transaction submission,

Hello,
I have recently submitted a capital gains real time transaction but have realised that I made a mistake in the submission.
The submission reference number which I received does not start with "RTT".
When I tried to update the transaction capital gains real time report online, and entered the submission reference number, it did not work (it says "Enter a valid report reference number").
Is there any other way to amend a capital gains real time transaction submission, and if yes, how?
Could you advise please

Hi
If you need to make a change, you’ll need to submit a new report, using your report reference number starting with ‘RTT’.  You’ll be sent this number by email after you first use the service.
This Guidance is available at the bottom of page: Report and pay your Capital Gains Tax: If you have other capital gains to report
Thank you