We have vendor since 1 year & start to sell some items to this vendor. What is the best way to register the new transactions?

You need to open same vendor with new transaction just update the details, no need to create a new account.

By planning,coordinating,organizing all resources for the achivement of the business.

But here the broblem is how to create an invoice for vendor in the system if the system not allow to do this ...!!!?

 

It is better to open another register (new) for the new transactions

 

 

It is always recommended to book all the transaction of same vendor in the same account it will create the history of Sales transaction and will give the complete information of the vendor.

 

So the new account should not be created and instead record the entries in the Old account. 

Its better new maintain the previous account.

For any vendor, you have to open new register and record entries carrying forward the account to new books after completing an year.