GST Invoicing Method for Service Upgrade

Dear All,

Would request your views on the correct invoicing method for service upgrade packages. Let me elaborate further:

We at Indiamart provide online subscripttion services to customers for advertising their products. When a customer purchases a package of say, Rs 100 for 1 year we collect the money upfront and issue an invoice of Rs 100 + GST. Now lets assume the customer opts for a upgrade (means higher package with additional features) after ,say, using the services for 6 months and the price of new package if Rs 200 for 1 year.

Current invoicing method: We issue a credit note of Rs 50 + GST against the old service, collect the balance amount from the customer (which is Rs 150 + GST) and issue a new invoice for Rs 200 + GST.

Proposed invoicing method: We propose to just issue a new invoice for Rs 150 + GST and don't issue any credit note.

Please let me know if the proposed method of invoicing sounds good.

PS: The GST rate for all our services is 18% only and the packages are different versions of online advertising.

Thanks