I have a AWS certificate with name *.example.ai, I can use same as portal.example.ai. But Now I want to use stage.portal.example.ai. As per AWS documentation it is not possible. is there any work around possible like if I create a certificate like *.portal.example.ai ? Then what about the route 53, which is having hosted domain as example.ai.
For the ACM certificate you will need to create a new ACM SSL. You can create it with multiple domain names if you want them to be shared or could create one for this.
The ACM domain would need to be for either stage.portal.example.ai or *.portal.example.ai if you want to wildcard this domain.
For Route 53, you can add this domain to your public hosted zone just like you'd create any DNS records. If you use the console you would specify stage.portal for the stage.portal.example.ai domain.