A receipt has to fulfill certain conditions set by the accounting integration before it will export successfully. If it doesn't, it will get an "Export Failed" tag after you attempt to export it.
The reasons for the export failure can vary, ranging from GST >10% to the GL code (aka account code) not being valid. The way to find out is to read the error message attached to each receipt, which can be found in the Notes section of each document.
Most export error messages are self-explanatory. For instance, in the case above, the receipt will only export if the tax is adjusted as recommended. If you get an error message that you'd like help with, please contact us on 1300 001 333 or email us at firstname.lastname@example.org