Commands in FFXIV are case-sensitive.

/ac "jump" <t>

will not work, but the following will:

/ac "Jump" <t>
/ac Jump <t>

The latter works because Jump is a one-word ability or item. In general, /ac, /equip, and /eaction are all very specific and require that the item or ability is typed exactly as it appears in the Inventory or Actions & Traits window.