[Error] Update error-1016.mdx (#24179)

* [Error] Update error-1016.mdx

SPM-2107

* Adjust capitalization and remove extra line break

* Update src/content/docs/support/troubleshooting/http-status-codes/cloudflare-1xxx-errors/error-1016.mdx

---------

Co-authored-by: Rebecca Tamachiro <[email protected]>

Author: ngayerie

src/content/docs/support/troubleshooting/http-status-codes/cloudflare-1xxx-errors/error-1016.mdx

@@ -16,7 +16,6 @@ Common causes for error `1016` are:
 - A CNAME record in the Cloudflare DNS points to an unresolvable external domain.
 - The origin hostnames (CNAMEs) in your Cloudflare [Load Balancer](/load-balancing/) default, region, and fallback pools are unresolvable. Use a fallback pool configured with an origin IP as a backup in case all other pools are unavailable.
 - When creating a Spectrum app with a CNAME origin, you need first to create a CNAME on the Cloudflare DNS side that points to the origin. Please see [Spectrum CNAME origins](/spectrum/get-started/#create-a-spectrum-application-using-a-cname-record) for more details.
-- There is no DNS record for the hostname in the Cloudflare for SaaS target zone.
 - There is no DNS record for the hostname in the target [Partial (CNAME) setup zone](/dns/zone-setups/partial-setup/) of a Workers subrequest ([Fetch API](/workers/runtime-apis/fetch/)).
 
 ### Resolution
@@ -26,3 +25,23 @@ To resolve error `1016`:
 1. Verify your Cloudflare DNS settings include an A record that points to a valid IP address that resolves via a [DNS lookup tool](https://dnschecker.org/).
 2. For a CNAME record pointing to a different domain, ensure that the target domain resolves via a [DNS lookup tool](https://dnschecker.org/).
 3. For a Workers subrequest to a Partial (CNAME) setup zone, ensure that the hostname exists on the Cloudflare zone (and not only at the authoritative DNS).
+
+## Error 1016 in the context of SSL for SaaS
+
+Cloudflare returns a `1016` error when the [custom hostname](/cloudflare-for-platforms/cloudflare-for-saas/domain-support/create-custom-hostnames/) cannot be routed or proxied.
+
+### Common cause
+
+- Custom hostname ownership validation is not complete. 
+- Fallback origin is not [correctly set](/cloudflare-for-platforms/cloudflare-for-saas/start/getting-started/#1-create-fallback-origin). 
+- A wildcard custom hostname has been created, but the requested hostname is associated with a domain that exists in Cloudflare as a standalone zone. 
+- There is no DNS record for the hostname in the Cloudflare for SaaS target zone.
+
+### Resolution
+
+1. To check validation status, run an API call to [search for a certificate by hostname](/cloudflare-for-platforms/cloudflare-for-saas/start/common-api-calls/) and check the verification error field: `"verification_errors": ["custom hostname does not CNAME to this zone."]`. The error will be resolved once the status is `active`.
+2. Confirm that you have created a DNS record for the [fallback origin](/cloudflare-for-platforms/cloudflare-for-saas/start/getting-started/) and also set the fallback origin.
+3. The [hostname priority](/ssl/reference/certificate-and-hostname-priority/#hostname-priority) for the standalone zone will take precedence over the wildcard custom hostname. This behavior applies even if there is no DNS record for this standalone zone hostname. Use a specific hostname instead of a wildcard or [remove the standalone zone from Cloudflare](/fundamentals/manage-domains/remove-domain/).
+4. Make sure that each hostname that needs to be served by the Cloudflare for SaaS parent zone has been added as an individual custom hostname and has the status `active`.
+
+