Added materials with datapack cannot be used when, in JEI in renders it as a blank column:

Example alloy recipe:

{ "type": "tconstruct:alloy", "inputs": [ { "tag": "tinkers_things:molten_hematite", "amount": 50 }, { "tag": "tconstruct:blazing_blood", "amount": 50 } ], "result": { "fluid": "tinthrudim:molten_enderium_alloy", "amount": 90 }, "temperature": 1500 }

Result (molten hematite is on the left):

The recipe is working exactly as intended. There is no tag named tinkers_things:molten_hematite, thus when you ask for it in the recipe you get nothing. If you wanted use hematite, you need to request a fluid, not a tag, using the key name instead of tag. This is fully consistent with how item based recipes work.

If you are wondering why the tag does not exist, well, just something I never needed so I never created. We use tags mostly in tinkers as we like to have the recipe match both still and flowing, but practically speaking you will never see a "flowing" fluid in a tank so its not needed. Don't let me creating the tag cause you to not learn why your recipe is wrong, understand the difference between a tag input and a fixed fluid input.

tl;dr: user error, the tag probably should exist but is not necessary to use the recipe/can be added by you if desired

Oh, ok, Ive got it. I just couldn`t find a proper key for it, when I searched for samples, trying to fix it.
The funniest part is that I found out how to put a tag from liquids from my mod, earlier, than what key should I use

Thank you for clarifying, still