send each collaborator a link to their own part of the song and let them confirm it, or tell you what's wrong, themselves. you stop being the go-between, and each person's yes is recorded against the share they agreed to.
a spreadsheet goes round, someone edits a copy, replies get buried in a thread, and three months later nobody knows which version was agreed. the person doing the chasing becomes the only record, and memory is not a record.
each person sees only their own part. they give one clear answer: yes, or what's wrong. the answer is kept with their name and the date. people who haven't answered get a reminder, so you don't have to send one.
right after the session, while everyone remembers it. again before release if anything changed. and any time a split changes, because a new split needs a new yes.
on the song page choose "ask [name] to confirm", or ask your AI to do it. pica emails them a link. they sign in with a link sent to that address, with no password, and confirm their writer share, recording credits and master share in one tap. if something's wrong, they reply to you, or mark a credit as disputed on the song. pica sends reminders. the song page shows who has confirmed, who it is waiting on, and anything disputed.
they sign in with a link sent to the email address you asked. if they are new to pica, that creates an account for them. there is no password to set.
the song and their own parts of it. if you allow it, they can listen to the recording too.
they tell you, and they can mark the credit as disputed. it shows as disputed on the song until it is sorted out, and the split doesn't lock.