The short answer to your questions are:

Account 27794 is a general ledger account number in the liabilities section (what you owe) of your chart of accounts but it does not exist.  In my highly modified copy of the sample file, I don't have any account between 27000 to 33000.  For testing you need to pick one that exists.

Therefore you picked 12000 but the rules of double entry bookkeeping indicate that if you are using an account that is linked to a subjournal, you must use the subjournal to post the entry.  Accounts Receivable Account 12000 is the linked account that controls how much customers owe.  You need to post using a Sales invoice or Receipt to update this account, but you are importing a General Journal entry.  If you open the General Journal module and look at the accounts available, you will see or in this case, not see 12000 Accounts Receivable.  Therefore you cannot import to it either.

Now let's look at the logic of your entry.

TSD it said:

07-03-15,"338", "Lowland Brewery Inc."
27794,105.00
23100,-5.00
50200,-100.00

This entry above Debits a 27794 liability account reducing it's balance, debits the 23100 GST Sales Tax Charged account reducing it's balance (and how much is owed to the government for this sale) and credits an 50200 expense account for Inventory Hardware reducing it's balance.  To me this sounds more like a purchase entry not a sales entry based on the accounts you are using but the entry appears to be a credit purchase entry giving the money back to you from a vendor.

Using the Sample file and assuming the customer paid for it at the time of sale, the following entry should import into the sample file.  Don't forget to look at the reports to make sure it changes the accounts the way you think it should change them.

Richard S. Ridings said:

07-03-15,"338", "Lowland Brewery Inc."
10600,105.00
23100,-5.00
40200,-100.00

Now if the customer does not pay for it and you are not wanting to track what is owing on a customer by customer basis, then importing as a General Journal entry is ok but you need to use an Accounts Receivable account that is not linked to the Sales module.  In the sample file, I would create an account in the Chart of Accounts like 12050 Accounts Receivable Imported (or whatever name you want), with the Account Type Subgroup Account.  You can ignore the rest of the tabs in the setup for import testing purposes.

Richard S. Ridings said:

07-03-15,"338", "Lowland Brewery Inc."
12050,105.00
23100,-5.00
40200,-100.00

This entry above will import for you with the new account and you can see the balance owing on the Balance sheet as well as the sale on the Income statement.  Note, you will not see a report of which customer owes what amount using this import method but you will see the customer name in the General Journal Report (Transaction Details).

For your entries in your real file, you will want to make sure you copy your real file and test on the copy first before doing imports on your live file.  The basic rules are the date format must be mm-dd-yy US format, all debits must equal all credits, negatives are credits.  The dates have to match either the current or previous fiscal year of your company file, so at this point in 2017, you probably cannot use 2015 on your real file (once you have one set up).

You can get a little more complicated than this if necessary (line comments, tax codes, project allocations and departments).

Hope this helps

Good morning Richard,

Thank you for this answer.
I hope I understand this right that if I import this type of file, I will not see on customer level that there is an invoice imported.
What do you recommend to use as import file to get an invoice in SAGE but without all the details. Statements and payments will be made/booked in Sage, the details of the invoices will be available in the other program.

Should I use an .imp file to import invoices ? Where can I find the file definitions of this file type? Or, yes I'm cheeky, can you make a file for me? One of my concerns is how Sage will know for which customer the invoice is. Will this be on company name or...?

Hope you can help me.

Ok, I'll be cheeky too. Go to the top of this website page where it says Search Sage City and type in "imp" no quotes. I'd be surprised if you can't find the format.

In your case, I would only use one line item though you should use a service item code of some sort because you can more automate it. On the customer ledger you can specify that the customer uses the same item codes as you do, so that you don't have to answer questions to indicate the item codes match.

Watch the tax code setup as you have to set up a code for each calculation. One of the responses in the searched threads from above, will give this as an issue.

Once you have a format that you think should work, and if it doesn't, post it and I'll let you know how to fix it.