How to import a file/data to GP 2010 SP4


so my company is selling a web based software that automates account payables.

we have a new Customer using Microsoft Dynamics GP 2010 SP4 11.00.2292 but we do not have a connector build for our system to exchange with Great Plains.

our system can give xml or csv files as output and we would need to be able to reimport all that data into GP so they won't have to re-key anything by hand in the Payables Transaction Entries of GP.

What can we use to import data in GP? which format do we have to respect?

It's our first time dealing with this software so we don't have a lot of information...

any help would be welcomed!