I am trying to customize the create collection wizard in AEM 6.4.5 to add a few more custom fields.
I have overlayed "/libs/dam/gui/content/collections/createcollectionwizard" to add the custom fields and also modified the collections metadata schema to add the custom field to the collection property. While creating the collection, the custom fields are visible and I can add the values but they dont get saved in the collections node.
Did you apply the modified metadata schema to that specific collections folder via "Apply to Folders"?
In addition to that, check if the triggered POST call includes your custom fields - open Developer toolbar via F12 or Ctrl+Shift+I > Click on Network tab > XHR tab, check the POST call to /content/dam.html and validate its form data