Hi there,

Javay here - from Calendly’s Developer Support team. Thanks so much for reaching out and for clearly outlining your use case — I completely understand why being able to lock certain fields like email or customer ID would be important, especially when the data is already verified on your end.

At this time, while Calendly does support pre-filling fields like name, email, and up to 10 custom questions using URL parameters or through the embed code, there isn’t currently a built-in way to make those pre-filled fields read-only or non-editable for the invitee. This includes standard fields (like name and email) as well as custom invitee questions (like customer ID or brand).

We’ve seen other users request this functionality as well — for example, to help prevent manual edits, reduce entry errors, or avoid misuse. While it’s not something the platform supports natively today, our team is actively tracking interest in this feature.

In the meantime, here are a couple of suggestions that may help:

• Continue pre-filling fields to save your users time and improve accuracy. While they can still edit the values, this approach does reduce friction overall.

• Validate post-booking: If you're passing data like customer ID or email from a known source (like a logged-in session or CRM), consider cross-checking submitted responses after the booking is made to flag or follow up on unexpected changes.

• Routing forms do support pre-filling and can be auto-submitted to direct users based on known info — though, as you mentioned, the final event booking form will still allow editing.

Since this functionality is important to your workflow, I’ll go ahead and submit this feedback to our product team on your behalf so they’re aware of your specific use case and needs.

If you have any further questions or want help exploring additional options, feel free to reach out to our team directly at support@calendly.com — we’re happy to assist!