I am using wpultimo which is a plugin which support auto map a domain on a subsite of multisite.
You might like check it at https://wpultimo.com/, or check the document at https://help.wpultimo.com/article/275-getting-started-with-domain-mapping-in-wp-ultimo
Before mapping a domain, it require setting a A record and CNAME record on DNS setting of mapped domain.
The site with original domain is created by Wordops and forced-ssl is enabled. Problem is that we can successfully map the custom domain on a subsite, but it will show "Error establishing a database connection" when we access the mapped domain:
1# is it possible to auto issue a mapped domain by wordops?
2# Or, anyway to allow sharing the ssl certificate to mapped domain?