Could not add website
Webmaster add-site flow shows webmasterPage.errors.addSite when create fails (API error or network).
Why this happens
Validation error (URL/category), duplicate site, program disabled, or server failure. Category messages may appear first when sanitize throws.
Diagnose and fix
1. Fix category/title/URL validation errors if shown; then resubmit.
2. Confirm Webmaster program is enabled and the user is approved as webmaster.
3. Check for duplicate URL already pending/approved.
4. See Webmaster sites and verification and Webmaster websites approval.