In the text for Sterile merit in M20 Book Of Secrets the Sterile merits description reads as such.

For some physical reason, you’re unable to sire or conceive children. Whether this is a Merit or a Flaw depends upon whether or not you want to sire or conceive children. Generally, this sort of condition can be easily cured with a little Life-Sphere magick; in your case, though, it can’t be rectified until and unless you, the player, discard the Merit or pay off this Flaw.

But there are no mechanics provided for paying off flaws. Are there any such mechanics in another book and if so what are they?

The description of the Sterile merit in M20 Book Of Secrets reads as such:

For some physical reason, you’re unable to sire or conceive children. Whether this is a Merit or a Flaw depends upon whether or not you want to sire or conceive children. Generally, this sort of condition can be easily cured with a little Life-Sphere magick; in your case, though, it can’t be rectified until and unless you, the player, discard the Merit or pay off this Flaw.

But there are no mechanics provided for paying off flaws. Are there any such mechanics in another book and if so what are they?