Mixed it up with is a colloquial expression that means to get into a fight, argument or misunderstanding. The antonyms for this phrase would be terms that convey calmness or peacefulness such as reconcile, understand, agree, or compromise. These opposites denote an amicable atmosphere in which people reach a consensus, resolve their differences and avoid unnecessary conflicts. It's a more desirable outcome than the opposite of mixed it up with, which might refer to fighting, arguing, or even suing each other. Instead, choosing to resolve your differences amicably would lead to a more harmonious and productive outcome.