You have the following options to enter address:

Fill in respective fields: Street, Postcode, City

It works well in ISPadmin yet it is more efficient and accurate to use

Google maps

Insert street and city, or street and postcode and click on Search above Google maps frame. Red pointer will be displayed directly on your selected spot, and also GPS coordinates will be fetched automatically. You may move around the pointer freely and place it on desired spot thus again updating fetched GPS coordinates. If you wish the client to be displayed in Other Map leave   Show on map checked.