QB Issue Resolution:

If by invoice you mean the vendors invoice to you his customer, which in QB is your bill

maybe

check in company settings to see if you have reimbursed expenses (I do not have a UK version of QBO to look at)

If you do, in the US it is gear>settings>company settings>expenses>bills and expenses and turn on make expenses and items billable
check mark to track billable expenses and items as income
then in company settings>advanced>chart of accounts click the edit pencil and select the billable expense income account

Why intuit separated the two related settings is anyone’s guess

When you enter a vendor bill/CC charge/etc, you will see a Billable check mark box, check that and select the customer name in the customer block. The next time you invoice your customer, the system will ask if you would like to add the bill to the invoice.  IF you do not want to add the bill to the invoice, leave the billable check mark box blank, the cost of the expense will still count against the customer

Resolution for Issue 'Is there a way of allocating specific invoices to specific jobs/ customers?' available: Yes (Solved).
Source: Intuit Community forum.

Is there a way of allocating specific invoices to specific jobs/ customers?: this issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.

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