Tagging some folks who might be able to help ye out here: 

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Casting a wide net since this is pretty specific stuff.

Christine Mikhaiel‌ - 

I am not vary familiar with Microsoft Dynamics GP, but if there is a service layer, you can definitely leverage that to perform your updates.

I would check out Web Services for Microsoft Dynamics GP  as a starting point and go from there.

What version(s) are you using for Nintex? SharePoint?

Thanks ‌

Thanks ‌. I'll check the link out. 

It is SharePoint/Nintex 2010 and very soon this year (after we implement this one), we will be moving everything over to O365.

We ended up dealing with it as any other application with SQL server as its database. I used sql action on the form to pull a list of active vendors from GP. And then at a certain stage we are creating transactions/batches.. all that fun stuff through stored procedures and executing those stored procedures on the query sql action - one stored procedure at a time. 

Also that was our only option since the web services were not installed. 

In the future, we might look at getting "Scribe" as an integration API, but the sql and the stored procedures did the trick for now, plus it is more manageable for what we are trying to do which wasn't really much.