Error Message: The line total does not match the expected line total
It can happen that your Magento store and Xero account don't agree on the same way of dealing with a certain order (mostly tax configuration). We try our best in the integration to level this out sensibly.
To work out why it doesn't like this particular order can you please do the following:
Under System > Configuration > Fooman Connect enable logging also enable logging under System > Configuration > Developer
Once enabled please go to Fooman Connect > Xero Orders manually mark the attempted but failed order and choose 'Export Selected' from the actions dropdown menu.
It will likely not go through - it however creates some additional log entries. Please email us the log from var/log/xero.log so we can take a look into this further.