GSTR-1 is a monthly return that summarizes all sales of a taxpayer while GSTR-3B is a monthly self-declaration that has to be filed by a registered dealer by the 20th day of the succeeding month.
Quarterly filing of GSTR-3B has been allowed for businesses with a turnover of up to Rs. 1.5 crore. The same for the period July-September should be done by 31st December. For those exceeding Rs. 1.5 crore, businesses will have to file GSTR-1 for July-October by 31st December.
Read more ↓GSTN had previously provided taxpayers with the functionality to claim a refund on the export of services with tax payment, Input Tax Credit(ITC) accumulated due to inverted tax structure and on account of supplies made to SEZ unit/SEZ developer.
Source:- goodreturns