@David111
Legally binding under what court system and subject to whose penalties?
In the USA, due to First Amendment Considerations…secular courts would be loathe to enforce a religious contract and could not fine or imprison a party to such a contract for non-performance.
In my area of CT, I am a Family Law Attorney and in the past 20+ years I have got Superior Court judges to approve divorce settlement language that states which party shall pay for the Beis Din/Get, but not language to require a Get be issued. They accepted my argument that the payment is merely contract law, not religious law. A party found in contempt is then subject to penalties as permitted by secular law.