Due or receipt basis

Dear All, We are Pvt Ltd Company. We provide & received services. We have made 4 invoices, against which we will receive payment against 2 invoice this month & rest 2 invoice we will receive after 30 days ie in January. My Question is that whether we need to pay tax on 2 invoices (on which we have received payment) or we need to pay tax on all the 4 invoices on due basis. Thanks in advance.