Reverse charge with credit

Hello all,

We get a credit / proceeds for scrap delivery §13b.

The credit note is written net price - we get from the supplier.

We have to calculate the tax from the net

Creditor 100€
Ledger (Other incom) 81€
Ledger (tax account) 19€

How can I translate this into SAP?

Currently the tax base amount is € 84.03 instead of € 100

regards M