Start with the evidence
Read the agreement for the document currency and apply it consistently to rates, totals and payment references. Keep an amount converted for internal discussion separate from the amount actually being invoiced.
Work through the example
USD800 and EUR800 are different amounts even when their digits match. In this example the agreement specifies USD, so both the line rate and the document total carry that currency rather than a bare symbol.
Make the next step clear
Review the exported document as well as the editable draft. If one label is missing, correct the presentation without silently converting the amount. Confirm any requested change of currency with the relevant person first.
Keep the source context
Treat an invoice draft as a description of an agreed business event. Keep the source agreement nearby and distinguish document preparation from approval, sending and receiving payment. These are separate steps even when they happen close together.