SERVICE CREDIT NOTE accounting document not posted

Hi Guys,

I am getting an error while posting service credit note in which the transaction currency in DMR & Inv is EUR.

While credit note, accounting document is not getting created. I went through the OSS note, which said to maintain account in OBYY for tax exchange rate differences.

ERROR :

Acct determination for Tax exchange rate differences with keys not defined in ch/acts

I didnt understand the explanation. Can you guys explain the reason behind it ?