The Poskim discuss whether one may submit a bid during the week for an online auction that will take place on Shabbat. Does a winning bid constitute "Mekach U’Memkar"-business transaction on Shabbat? The Poskim conclude that it is permitted, since the acceptance of the bid on Shabbat is not the consummation of the transaction. At that point, the winner merely becomes obligated to pay his bid at a later date. Alternatively, there are platforms in which he already made his commitment in the contract at the time of the bidding, before Shabbat. However, it is prohibited to participate in an online auction, in which the bidder pre-programs his account to submit the bid on Shabbat.
It is permitted to place a bid before Shabbat in an online auction that will conclude on Shabbat.