Reparation to whom? The victim of your bad act? God?
It’s not needed for absolution. All that is required for absolution is that you repent of your sin - are sincerely sorry and firmly resolve to sin no more in the future.
The priest can’t order you to make reparation and then come back for absolution, unless somehow by “reparation” you’re ceasing to commit an ongoing sin. For example, if you stole somebody’s car and are driving around in it, then if you resolve to sin no more in the future that might mean you need to return the stolen car so you’re not continuing to commit car theft. In that case the priest would make you stop driving the stolen car before he could absolve you, but not as “reparation”, instead it’s to stop the ongoing sin.
The priest can’t order you to do anything that might disclose your sin outside the confessional (for example, pay back stolen money, or tell your spouse you cheated). To the extent the priest might be able to give you some penance that involves reparation (for example, saying prayers), nowadays this would happen after he absolves you.