Type Soul carries ten item types on the sell form, and an offer picks exactly one of them. The ten are Buddies, Emblems, Essences, Soul Blessings, Warp Dust, Skill Boxes, Rerolls, Vows, Shards & Fragments and Other. Pick the label a buyer would hunt under, then open the Type Soul items marketplace to see how that group is trading right now.
Essences and Vows
The two groups tied to what a Soul Reaper becomes. Both are bought by name, which is why they sit in separate item types rather than under one progression heading. Write the exact name into the offer.
Rerolls and Skill Boxes
Sold as a countable stack. A Reroll is another draw and a Skill Box is another opening, so the number you deliver is the figure a buyer will price against. Neither one settles what comes out.
Warp Dust and Shards & Fragments
Supply that gets consumed rather than kept. Cards in both groups live on the amount they promise, and an offer that leaves the quantity vague loses to one that prints it.
Buddies, Emblems and Soul Blessings
Single pieces, each posted with the buddy, emblem or blessing written out. None of the three is an amount, so none of them gets compared per unit against the counted groups.
Other is the tenth label, and it takes event pieces and seller-assembled lots that none of the nine named groups fit. It also carries the most risk of a buyer reading something different from what you meant, so the description has to do all the work the item type will not. Both fields are filled on the item listing form.