Input tax credit

if the payment is made in instalments you can take itc on last payment 

otherwise you can take input on payment

what is notification no. 76/2018 central tax and 75/2018 central tax

Normally, ITC is taken on basis of ‘Electronic Credit Ledger’. However, if advance 
payment was made before receipt of goods and services, input tax credit cannot be 
taken as goods and services are not received. 
At the time of payment of GST on advance, the supplier of goods and services cannot 
issue tax invoice. He has to issue only ‘receipt voucher’.

Input tax credit is available only if goods or services are received with invoice document.