2 different tax rates were used

What causes this issue?

You are entering a posting in foreign currency. In doing so you
manually enter document and local currency amounts. The amounts entered
for taxes thereby produce a different tax percentage in the document
currency as in the local currency. This is not permitted.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Correct the tax amounts in document or local currency, so that the
ratio between the tax amount and the tax base amount, in both document
and local currency, is equal.

Error message extract from SAP system. Copyright SAP SE.