Orally or Verbally

Solution 1:

Verbally comes from Latin verbum, “word.” Its adjective form verbal is often used in the sense of “spoken,” and contrasted with “written.”

Orally comes from Late Latin oralis, which comes from Latin os, “mouth.” It means “by mouth.” Like verbally, orally is sometimes use in the sense of “spoken”.

From Grammarist.com:

English authorities have traditionally urged against using verbal in reference to spoken things—for example, verbal/oral communications, verbal/oral reports, and verbal/oral warnings—but verbal is increasingly used in these phrases, perhaps in part due to oral‘s prurient associations. But oral is still a good word, so one does not have to follow the trend toward favoring verbal. Still, using verbal in the newer way is not wrong, as it is sanctioned by common, widespread usage and is by no means new.

I think Verbally is more suitable though.

Solution 2:

Oral is perfectly acceptable in the context by current AmE usage.

o·ral ˈôrəl/ adjective
1. by word of mouth; spoken rather than written.
"they had reached an oral agreement"
synonyms: spoken, verbal, unwritten, vocal, uttered, said, by mouth, viva voce
"an oral agreement"

Also on ODO.

Oral = verbal