How do I read the 上? うえ? or じょう?
What is the meaning of 上 in that sentence?
「上」 is read 「うえ」 in that context.
「～～の上（で）」 means "based on ~~". The ~~ part acts as a premise or condition in performing an action. The ~~ part usually describes an understanding or agreement of some sort.
= "Please place orders upon agreement and acceptance of (what has already been explained)."
うえ=on.In english,after～ condition～ understanding～ on～(this is best similiar word to 上).ご了承の下（もと）is same meaning.
The reading of 上 in this case is うえ and it means "after" in this case.
ご了承の上 is translated as " after agreement".