Expense for ESTA - what city of purchase ?

[MEW]

HI all, my first post

I have purchased an ESTA for travel to USA for business (purchased on Travel & Expenses card)

I have to state "city of purchase". I have looked long and hard and cannot find online or on the documents what to put for this

Please advice

Thankyou

[MEW]

I am thinking to put Washington DC as this is the HQ for US Customs and Border Protection