You need to create a ticket via Admin Console.https://helpx.adobe.com/ca/enterprise/using/support-for-enterprise.html 

You'll need to install it using the cloud manager pipeline.Refer: https://github.com/adobe/aem-guides-wknd/tree/aem-guides-wknd-2.1.4  

https://experienceleague.adobe.com/docs/experience-manager-cloud-service/content/overview/seo-and-url-management.html?lang=en#building-an-xml-sitemap-on-aem explains how to create custom Sitemap along with best practices for URLs.

https://experienceleague.adobe.com/docs/experience-manager-dispatcher/using/configuring/dispatcher-domains.html?lang=en explains how to configure Multiple domains in dispatcher.

https://experienceleague.adobe.com/docs/experience-manager-learn/assets/dynamic-media/images/smart-crop-feature-video-use.html?lang=en will be helpful.

Sub-asset generation can be very resource intensive on any Experience Manager deployment. If you are generating sub-assets when complex assets are uploaded, add the DAM Update Asset workflow step. If you are generating sub-assets on-demand, you can create a separate workflow to generate sub-assets. ...

 Validate both the accessToken and refreshToken using the curl command. 

Can you check if the asset is published?

https://experienceleague.adobe.com/docs/experience-manager-cloud-service/content/assets/admin/translate-assets.html?lang=en will be helpful.

Check logs for any error.