GSTR 3B is a summary of all your invoices for a particular. GSTR 3B needs to be filed
every month by the 20th of the following month. For example - Invoices raised in Jan
2020 need to be summarized and filed on or before 20th Feb 2020. GSTR 3B contains input
tax credit claimed, GST liability to be paid, reversal charges if any, etc.
GSTR 1 is filed either monthly or quarterly. GSTR 1 contains invoice wise details of
every sale along with the tax liability. This helps your customer to take the eligible
input tax credit.