[talloo]

Most consulting contracts are work for hire where you explicitly agreed to transfer and relinquish any claim to the IP.

You should check your contract to see what it says. In all likelihood, it is unreasonable to request royalties.

[codingclaws]

There was no written contract.

[codingdave]

Contracts do not have to be written. Whatever you agreed to verbally is your contract. So no, it is not reasonable to come back years later and ask for more money.

But in the future, it is a great idea to add into any new negotiations.