Either means one or other of two. Its use in the sense of each of two, as in:
On either side the river lie
Long fields of barley and of rye,
or in:
The concert will be broadcast on either side of the nine o'clock news,
is common, but, according to Fowler "is archaic and should be avoided except in verse or special contexts."
Either must take a singular verb. It is often wrongly given a plural one by attraction.
I am unable to trace that either of the items have been paid. (Have should be has.)