The webmaster program is not enabled
webmaster-sites threw The webmaster program is not enabled. when the program flag is off.
Why this happens
Same root as the “disabled on this site” UI string — this is the ops/API wording before site create/verify.
Diagnose and fix
1. Enable the webmaster program in admin settings; save.
2. Retry add site / verification.
3. If the program is on but the user is blocked, see This user is not approved for the webmaster program.
4. See Webmaster sites and verification.