Tax amounts have a different exchange rate to invoiced amounts

What causes this issue?

You have entered both local and document currency for the tax amounts
or for the invoiced amounts. The exchange rate determined from the tax
amounts thus deviates from the exchange rate determined from the
invoiced amounts.
This message can also occur if you are working in a company code which
permits an individual conversion for the taxes according to the posting
date or document date.

How to fix this error?

Correct the amounts if they were entered incorrectly. If the amounts
are correct, note that the different exchange rates are also to be
taken into consideration with offsetting entries since a document
balance might otherwise be created in local currency.
If the warning comes about due to an individual conversion of the tax
amounts, then it can be ignored since then the difference in local
currency which results can be charged off automatically. The message
can then be suppressed using customizing.
INCLUDE 'CUSTOMIZED_MESSAGE_INFO' OBJECT DOKU ID TX

Error message extract from SAP system. Copyright SAP SE.