If you have not had a form of payment added to the account previously this will still have needed to be added before the 15th of the month.
So if this has been added after then payment will be at the end of the next month, as long as you have met the payment threshold and your tax information is filled in.
The upcoming payment will show in your in your payment history (Person Icon top right of dash> Payments and Charges> Payment History) around the 4th-6th of the next month. So your first payment will be at the end of April if you have just updated your form of payment after the 15th March. 🙂