Amend return/Remittance and SA-109

I have become aware that I failed to tick either box on question 8 SA-100 regarding claiming remittance basis, which was filed online through HMRC Self-Assessment. I do know that the SA-109 can not be filed with HMRC online. The question is, can I amend my file return online (ticking the yes box) and then separately mail SA-109 to HMRC? Or do I need to either amend and send the whole turn on paper, or purchase online filing software which includes SA-109 filing? Thanks

Hi Msilberb,

You need to send the whole return in the same format so either all on paper or purchase 3rd party software.

Thank you.