For the record, I have screenshots of BPT showing latest tax code on confirmation screen during FPS confirmation then writing an older tax code onto FPS data and payslip. I called the support number above and the HMRC representative said there was no way to report a software issue and that I did not need to take any action. I will refer back to this post should HMRC raise an issue in the future.
I have used BPT to submit FPS for employee payment. Received P6 Employee tax code change since last payment. New tax code was entered before entering new employee payment and Tax code confirmed correct under 'PAYE Details' section during FPS entry. However on examining the FPS document and payslip, the old tax code is still there.
I only noticed this after submitting- so FPS submitted has wrong tax code on it and it was impossible to correct it.
Employee is director, biannual irregular pay. AN method. New tax code entered in BPT today (13/02/22) for P6 received 26/10/21. FPS submitted for future payment on 07/03/22. New tax code is W1M1. Last payment was 10/10/2022.
Maybe this is because pay is biannual and BPT won't allow two tax codes in same period? However since pay is irregular it should be OK to make two payments at any time in the year.