"add new" join button not working. default relationship invalid

[andr-ec]

Describe the Bug

"add new" join button not working. when the button is clicked it brings up a modal, that modal has the wrong relationship preselected.

clicking save, then fails. seems like it's related to the preselected value being a string and not an int.

Link to the code that reproduces this issue

https://github.com/andr-ec/payload-bug-reproduction

Reproduction Steps

Go to Users collection, edit the existing user. click on the "add new" button next to the "medias" join field.

the model will pop up, add the alt field, click save.

The save will fail.

if the user unselects the relationship and reselects it manually, it works.

Which area(s) are affected? (Select all that apply)

area: core

Environment Info

Payload: 3 stable
nextjs 15.0.0
nodejs: v23.2.0