Can't Add Fields to collections/all

The page at /collections/all Vs. Other Collections

Shopify differentiates the page at /collections/all from all other collections. For this reason, Custom Fields needs to treat them differently as well. Shopify does not allow us to add fields to the special collection located on your site at yoursite.com/collections/all

In order to add fields to that page, you'll need to use a clever workaround. 

No workaround is needed when adding fields to any other collection.

The Workaround for /collections/all

It's easiest to simply add one of the snippets below to your collections template which will handle printing of fields for both types of collections.

1.) Create a new collection in Shopify. You'll use this collection to attach your fields to, then reference that collection on /collections/all so it looks like the fields are attached to that special collection.

2.) Add some fields to Collections in the app.

3.) Edit your template called collections.liquid using these snippets as a starting point.

Additional Info

Shopify: Collections Documentation