Tab with my Custom Portal Dynamics 365

Damian_Dbrowski 
You can create app in developer portal and add static tab in app manifest.
In static tab section add your custom portal link in contentURL and in websiteURL.
Also add domain of URL in validDomains section of manifest.

{

"entityId": "personalTab",
"name": "Personal Tab ",
"contentUrl": "https://{{PUBLIC_HOSTNAME}}/<yourDefaultTabNameTab>/personal.html",
"websiteUrl": "https://{{PUBLIC_HOSTNAME}}",
"scopes": ["personal"]
}

Please refer below sample:
https://github.com/OfficeDev/Microsoft-Teams-Samples/tree/main/samples/tab-personal/mvc-csharp

Please refer below manifest:
https://github.com/OfficeDev/Microsoft-Teams-Samples/blob/main/samples/tab-personal/mvc-csharp/demo-manifest/tab-personal.zip

For creating app via developer portal, please refer below document:
https://learn.microsoft.com/en-us/microsoftteams/platform/concepts/build-and-test/teams-developer-portal

Thanks,
Nivedipa
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