Tax code & may only contain one assignment line

What causes this issue?

For direct postings to tax accounts, only <DS:GLOS.Steuerkennzeichen>tax
codes</> containing exactly one tax item may be used. Tax codes with
several rates or a nondeductible portion are not allowed here.

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?

Use a different tax code.
For direct postings to a tax account, you might have to define a
separate tax code for which only one line with a percentage rate other
than zero is active in percentage rate maintenance. All other lines must
be inactive.
For more information, see SAP Note 869540.
INCLUDE FI_NA_F5

Error message extract from SAP system. Copyright SAP SE.