Hi @SmithAdam198508 Congratulations on your tribunal win! These types of cases often take some time to get payment through: 6-8 weeks following the hearing is common. PIP will usually check the account details for payment before releasing arrears payments which is why you have had this letter. Often it has been a long time since the claim was started (months at least) and so they check the account details haven't changed since then. If you have returned this form I would allow 2 weeks and if you have not heard in this time then call them for an update.
As an aside, if you get any other benefits such as ESA, Housing Benefit, Council Tax Support, make sure you report the PIP award to the office that pays the benefit as this can sometimes result in an increase in these payments - this depends on the PIP award and your other circumstances of course.
Well done again!