Should I enter invoices for income issued on 1 October but for services provided in September in the Q3 or Q4 vAT declaration?

First time filing a vAT declaration, a few starter questions… I have an invoice for services provided in September but with an invoice date of 1 October. Now this income (and vAT) from Q3 will be included in the Q4 accounts. Should I take this invoice into account for the Q3 vAT declaration or simply pay the vAT in Q4 even though it concerns income from Q3? How should I adjust/enter this in Dexxter?

Thanks in advance.