Hi @yuriscom
Seamless SSO should be enabled by default on your tenant, the option to toggle it on/off is available for legacy tenants as mentioned in our documentation, meaning that your applications should have Seamless SSO between them if BOTH applications have the same database connection enabled. Otherwise, you may want to look into Silent Authentication if you want your applications to use different connections.
I would advise you to review this Knowledge Article regarding Seamless SSO.
If you have any other questions, feel free to let me know!
Kind Regards,
Nik