Free to use after signing up at aiva.ai, and the free plan has no trial clock attached. What it limits is downloads — a small number each month, short tracks only, MP3 or MIDI files only. No plan currently allows a track longer than five and a half minutes. Whether every creation mode is open on the free plan is not spelled out in AIVA's plan comparison, so you may need to check that once you are signed in.
Who owns what you make depends on which plan you are on, and that is the first thing to settle. On the free plan AIVA holds the copyright, use is non-commercial only, and you must credit AIVA with a link to aiva.ai. Standard (a paid plan, plus VAT, cheaper billed annually than month to month) drops the credit requirement and allows monetised use on YouTube, Twitch, TikTok and Instagram only — but the copyright still sits with AIVA. Only Pro, the higher paid tier, transfers the copyright to you and lifts the platform restriction. Read that split as the current position rather than a settled one: AIVA's licence agreement carries no effective date of its own and never says which plan maps to which licence, and the helpdesk article explaining the split is dated 2021 — so the live comparison table on AIVA's pricing page is the most current statement of what each plan allows, and it is the one to check before you rely on any of this.
Whether you need to pay is decided by what the music is for, not by how much you earn from it. A school project or a video for friends sits inside the free plan. Anything that promotes a business, or anything you want to hold the rights to, does not.