Return a voucher
GET
/ext/{siteid}/api/v1/voucher/{voucherid}
curl \
-X GET https://api.spotipo.com/ext/{siteid}/api/v1/voucher/{voucherid} \
-H "Authentication-Token: $API_KEY"
curl \
-X GET https://api.spotipo.com/ext/{siteid}/api/v1/voucher/{voucherid} \
-H "Authentication-Token: $API_KEY"