Every free Twitter scheduler pays X per post somehow. Here's who pays, and what it costs you.
X bills the app for every write: about $0.015 per plain post, about $0.20 when it has a link.
About $2.73 plain, $36.36 with a link, $39.09 with the link in the first reply. Links drive the bill.
Queueing is free. Credits are charged only when a post publishes, and refunded in full if X rejects it.
Light text posting: a free plan works. Daily links: budget for them. Can't miss a post: skip browser automation.
The full breakdown, with the per-post math.