There doesn't appear to be a way to specify metadata (eg: minecraft:wool:16) for payment items in Minebay using the config method of RecipeAPI. Specifying the metadata value as part of payment-item returns an error saying the item doesn't exist, and specifying the metadata value on its own in payment-item-metadata simply results in the non-metadata version of the item being requested.

This is because Minebay doesn't check on metadata for the payment item.
It could possibly be changed to use the same system as the other one-to-one recipes like the oven or freezer.
Currently it's an implementation and API limitation.

It would be nice if it did check metadata.

Closing since I won't be maintaining 1.12.2 anymore.