Say for instance journal 460 has 50 lines, but due to file length limitations only 48 are on the file and the remaining 2 get passed on to the next file

Do you know any programming languages? Really easy to do a splitter to cope with this in perl or python

I actually don't unfortunately. I do however have a basic exe that spits out 25k line csv's inc header

You can use integrator.io (Celigo) data loader free tier to import without splitting the file first

Thanks is that like a bundle/suiteapp I can install ?

Celigo's CloudExtend Excel can create NetSuite journal entries up to 10K lines each using an Async upload process (as opposed to 1K in the UI). Even then I think the difficulty will be in getting each of the entries required to get to your 300K lines to balance.

@Chris Corcoran did you mean Cloud Extend for Excel? Wouldn't integrator.io be able to do this?

@michoel thanks for catching this. Yes, updated to Excel. integrator.io should also be able to do this as could data loader. With the Excel App the advantage is everything stays in Excel, there is no need to create connections, flows, etc.