Application for relief at source from UK Income Tax – (Nil code)

I'm in the process to start to draw down on my non-PCLS (i.e.75%) taxable pension, held with an International SIPP in the UK this calendar year. Having followed the process based on UK-United States of America Double taxation Convention (NIL Code) for tax relief at source to establish a NIL code in the UK, and having subsequently been advise by the US-Inland revenue service that they have submitted the required certification of US residence to HMRC at the beginning of October 2023. I have been checking my Gateway account daily for progress since then, but have neither seen any acknowledgement of receipt nor progress to date. If anyone else has encountered this issue , please advise on the best way to follow up on this matter with HMRC, it would be greatly appreciated.

Hi

As a code to make your pension exempt cannot be issued until the pension is actually in  payment, nothing will have been done as yet.
You can phone to check we have your application thoough on +44 13 5535 9022.

Thank you

Thank you for your response. A test transaction was initiated from my SIPP in order to test whether the 'Nil' code had been implemented, it was not per the code currently assigned and viewable in my Gateway following my submission. I will call the number suggested to follow up on progress.