Is such phrase is correct?
A request was sent to somewhere.
Something is telling me that sentence below is correct one.
A request has been sent to somewhere.
Simple past passive voice (the first) and present perfect passive voice (the second) are both correct English.
If the you are reporting on this immediately after the request was sent, or if you particularly care about the impact upon the present time (e.g. the fact that the request was sent means that there is now a pending request being processed, which is important to know in terms of the current status), then use the second. Otherwise use the first.