Make another Credit Card Type of account and name it for the Vendor. Example: NAPA Auto Parts lets you carry inhouse Credit Line. This is Cardless Inhouse Charge Account tracking, in other words.
They take from your CC = Credit Card Charge, and post as the "expense" the Vendor Credit account. Or, that is a Transfer, from VISA to Vendor Cardless CC account.
Then, the Vendor 'uses" your account with them, so enter what you owe them as Credit Card Charges. Not what they Take from you, but what you owe them for Purchases made. There is no Bill; they are already handling this as inhouse charge account.
"Eg: Jan 13 - Amount debited 500 for previous bill"
Transfer $500 from VISA to "pay vendor charge account."
"and remaining unapplied payment 100"
That is the running balance you will see in your "inhouse" account.
"Jan 30 - Bill Amount 400"
Enter Purchase details as Credit Card Charge against the Vendor Inhouse Charge account. Now you show what you bought from them, and owe them for and owe them more.
"Feb 13 - Amount debited 450 for Jan Bill"
Transfer from VISA to Vendor Inhouse Charge account.
"How do i apply the amount 100 in the unapplied payment from Jan 13 payment and make payment for Jan Bill 400 and show the balance unapplied amount 150."
By simply tracking all of it using a Vendor Inhouse Credit Card type of account for the activities.
