The vendor portal
When you assign a questionnaire, the vendor answers it in a separate, secure portal, not in your SolveGRC workspace. This page walks through what your vendor experiences, so you know what to expect and can help if they get stuck.
Accepting the invitation
The vendor clicks the secure link in their email and lands on an account-setup page showing who invited them and what they've been asked to complete. They enter their name, set a password, accept the terms, and their account is created. From then on they sign in at the portal login.

The vendor dashboard
After signing in, the vendor sees a dashboard of the questionnaires assigned to them, with counts for Needs attention, In your hands, Replies needed, and Submitted / accepted.

Answering the questionnaire
The vendor opens an assignment and answers one question at a time, or switches to Section view to see a whole section at once. Save & next saves the answer and moves on. Answers also auto-save after 2 seconds, so nothing is lost if they step away. Where your team has approved one of their earlier answers for reuse, the portal offers it as Use previous answer. It never fills it in automatically.

Attaching evidence
The vendor can attach supporting files to an answer (a policy, a certificate, a report). They need to save the answer first before the uploader turns on. Each file can be up to 50 MB, with up to 10 files per answer. Uploads are closed once the questionnaire is submitted.
Each uploaded file becomes an evidence item on your side automatically. A malware scan runs after the upload. Only files marked Clean or Uploaded (not yet scanned) can be downloaded or sealed. A quarantined file goes to Evidence Review, where your team works it from the Review Queue tab with Approve Override, Delete Permanently, Rescan File, or Mark as False Positive.
Review and submit
When the vendor is ready, a Review and Submit page summarizes their progress, lists any required questions still unanswered with links to jump to them, and asks them to type their name as an attestation.

Completeness is enforced on the server, not just in the browser. If any required question is still blank, the submission is refused, so a questionnaire can't come back to you looking complete when it isn't.
Once submitted, the vendor sees "Submission Successful!" with a Confirmation Number, and the assignment flips to submitted on your side, ready for review.
For security, the portal keeps the vendor's session in memory only. If they do a full browser reload partway through, they'll be asked to sign in again (their saved answers are safe). Tell vendors to use the in-page navigation rather than reloading.
With a submission in hand, the work moves back to your team. Continue to Review and findings.