Can you cast a creature spell with convoke and tap creatures that have summoning sickness to pay for it?

Summoning sickness (the unofficial name for the rule under CR 302.6) restricts a creature from attacking or activating abilities that include the tap symbol (or untap symbol) in their activation cost — but only if that creature has been under your control since the beginning of your current turn.

Convoke (CR 702.101) is a keyword that lets you tap creatures you control as you cast a spell, with each tapped creature reducing the cost by one mana (or one mana of a color the creature shares). Crucially, this tapping happens as part of paying the casting cost of the spell, not as the activation of a tap ability. Because it is not an activated ability, CR 302.6's summoning sickness restriction does not apply.

The relevant distinction is in CR 302.6 itself: a creature 'can't attack, and its activated abilities with the tap symbol or the untap symbol in their activation cost can't be activated' if it has summoning sickness. Convoke is a static keyword that modifies how you pay for a spell — it has no tap symbol in an activation cost.

Example: You cast Siege Wurm (which has Convoke) on your turn. You just played a Centaur Courser this same turn (it has summoning sickness). You can legally tap that Centaur Courser to help pay for Siege Wurm's convoke cost, even though it couldn't attack or be tapped via an activated ability like with a Springleaf Drum.