Is it possible to purchase more units of MF under the same folio no.?
Yes, this is possible. This is what happens when you do an SIP the traditional way. However, when you do SIPs via Coin, different folios are created, but this should not matter to you as they are all in DEMAT form.
How to do that in coin platform.
When you invest in a particular Mutual Fund through Coin, a folio number is generated for this transaction by the AMC managing the MF. Although the statement of transaction with the folio no is not provided to you by the AMC for this purchase as your units are in Demat form with a unique Demat account number, you will be able to see the folio number in your Coin dashboard.
Any subsequent purchases made in the same MF will be mapped to the same folio number on Coin.