... "Please contact itunes support to complete this transaction" .How I can fix it ?
Contact iTunes Customer Service
... Is it possible to use only this Apple ID to buy in-app purchases for both account games "acc1" and "acc2".
See Here http://support.apple.com/kb/HE37
I have multiple Apple IDs. Is there a way for me to merge them into a single Apple ID?
Apple IDs cannot be merged. You should use your preferred Apple ID from now on, but you can still access your purchased items such as music, movies, or software using your other Apple IDs.