I've found a couple similar questions, but no answers (if there are answers that even exist).  I'm just going to see if any of you smart people can figure this one out. :) And thanks in advance for any help!

Pretty simply, I need the Gig Name (we've renamed 'deals' or 'opportunities' to "Gig", but it's simply the default opportunity-name field) to become read-only at the 'Sale Complete' stage.  It's not user based, and that won't fix my issue.  It's solely stage based.

If it helps to understand what I'm needing, here is the reason:  Once our deal/opportunity (aka gig) is 'Sale Complete', several webhooks are triggered that send data to Quickbooks, Quickbase (custom app) and a couple other external apps.  These connections are one-way connections, and in some cases, the gig-name is the lookup field.  So if/when we update certain things in CRM, those external apps (primarily Quickbooks and Quickbase) are also updated.  However, if my sales team or anyone else changes that deal name, future connections are lost and the respective apps don't update.  So the simple solution for me is to make the Deal Name / Opportunity Name become read-only once that Sale Complete stage is reached.

(For the record, if I can't accomplish this, I know the unchangeable unique field is the zoho id.... and that is what I SHOULD have used as the trigger for lookups in all cases.  But I didn't, because I'm a dumbass.  I used the Gig/Deal name in some cases. If I can't get this to work, I'll change things to rely solely on the unique zoho ID, but that's a LOT of work at this point; and I'd rather avoid that if I can simply trigger the deal name to become read-only at a certain stage of the client journey).

THANKS