Using latest version as of CurseForge today. Here's what I did and what happened:

• Open Krystel at the Summer Terrace (Spirit of Harmony Vendor)
• Right-click White Trillium Ore
• Type 200
• Press Enter
• Press "Yes" at the confirmation prompt
• (Ore received successfully)
• Right-click Black Trillium Ore
• (The vendor display is bugged: the text "Black Trillium Ore" no longer appears on the display, although the icon is there)
• (Nothing happens on right-clicking)
• Close and re-open the vendor. (The Black Trillium Ore now displays correctly.)
• Right-click Black Trillium Ore and type in 200, press Enter.
• Click "Yes" at the confirmation
• (Game freezes for about 5 seconds, and when it unfreezes, I still don't have the ore)
• Right-click Black Trillium Ore and click "Yes" - the box dismisses and no ore is bought.
• (I cannot buy Black Trillium Ore at all now).
• Disable Bulk Buy and reloadui, now I can buy Black Trillium Ore.

I have heaps of SoH, the problem is not running out of currency to buy.

Thanks for the report.

Unfortunately I don't play WoW any more, so I can't easily debug this myself. From the brief testing I've done with my trial-equivalent account, it seems to be working for gold purchases.

I've added some debug logging and released an alpha version here, can you please install this along with DebugLog, try to reproduce the issue and then post the CSV and HTML logs from DebugLog?