This issue is because of the way that your Xero account is set up. If you look in your Xero Settings, you will either see blank fields (All fields must be filled, even if you are not using this aspect of the integran) or one of the accounts set up will look something like the screenshot below:
As you can see, the Reference number is missing at the front of the Account Name.
This needs to be changed in Xero:
1) Log into Xero
2) Go to Settings – Chart Of Accounts
3) Click on the Account that is missing the code
4) Update the box called “Code” and click Save.
5) Return to Workshop Software and save the Xero integration.