Failure to pay agreed settlement in court

You don't say whether the settlement was embodied in a Court order, or was just an agreement between the parties.  If the former, it can be enforced through contempt proceedings.  If the latter, it can be enforced the same way as any other contract, i.e. you sue the other side for breach of contract.  The merits of the underlying dispute would no longer be relevant, however (except if the defendant claims that they prove some defense to the contract, such as fraud in the inducement or failure of consideration.)  You would only have to show that the settlement agreement was a valid contract, that you had performed your end of it, and that the other side had breached.  If you sue and win, you would get a judgment, which can then be enforced by collection procedures, such as garnishing wages or other income, auctioning off the debtor's assets, etc.