Multiple invoices into one invoice

We manufacture fertilizers and in many cases we have small farmers come to our place and pick good worth 3,000 to 4,000 . Though these are small transactions , number of transaction are high and its very cumbersome to enter each customer in our system separately with their customer ID, so what we do is we are adding up all the monthlly of these petty sales and raising one invoice end of the month and filling GST accordingly. Please advise if this  is OK as for us to enter each farmer separately will be spamming our ERP system, if our present system is OK, what precuations do we need to take to avoid future issues in GST. Most of the payments are thru GPAY and phonepe 

thanks