A prefill link transfers known booking details into the hosted signing flow. The participant still reviews the form, supplies required consent and signs. This is useful when you know a name or session reference but do not want to build a custom signature interface.
Create the link on your server
Use create prefill link with a key that has prefill:write. Values are checked against the active template version. Partial values are allowed; required fields do not all need to be supplied when preparing the link.
Unknown block IDs and malformed values return 422. Map booking fields to actual block IDs, and keep that mapping in step with published template changes.
Leave consent and captures untouched
You cannot prefill signature, initials, checkbox, guardian-consent, photo-capture or ID-capture blocks. Those fields require interaction in the signing flow. Do not infer a consent answer from the guest's purchase or use a stored image to bypass a fresh signature step.
The signer can edit allowed prefilled values. The actual submitted answers are what become part of the signed record, not an assumption that your booking values were accepted unchanged.
Choose a useful expiry
The default lifetime is 72 hours. The supported range is 1 through 720 hours, up to 30 days. Pick a duration that fits the communication schedule and tell staff how to prepare a new link if plans change.
A token is consumed when a waiver is successfully submitted, not merely when the page opens. Expired, used or unknown tokens lead to the normal empty signing form. Your guest instructions should still make sense if they need to type their details again.
Protect the URL
The link contains a private token. Do not publish it on a general website, include it in public analytics or paste it into a shared support conversation. Retrieve prefill link also requires prefill:write and returns expiry and usage information.
Use a non-sensitive booking tag when you need reconciliation. Test an edited answer, an expired link and a second visit after successful submission. Then follow the signed record through webhooks.