how to record an advance payment made for a sister company

Hi Team,

I have to record an advance payment made by my company to its sister company. I did a journal entry by crediting the cash amount and by debiting the cash at the bank. However when I enter the NAME of the sister company in the journal entry I realized that the sister company was recorded as a vendor and not a customer, thus I am unable to save the journal entry I made. I don't want to re-enter the company as a customer because there are a lot of expenses already recorded and I am afraid it would make it difficult to trace those expenses later on if I record the same company as a customer and as a vendor.

Is there another way to record this advance payment? 

Thank you for your help.

Meron