How to create a legacy M365 AppID/Secret -

!This is legacy code and my not work any more for your tenant.
Also this type of Client/Secret is not supported from version 7.0 and onwards of SMART Migration

Helpful links for creating an Office 365 AppID

Helpful links for creating an Office 365 AppID
Microsoft: How to create an Office 365 AppID Permission Request XML (Tenant wide permissions) `<AppPermissionRequests AllowAppOnlyPolicy="true"> <AppPermissionRequest Scope="http://sharepoint/content/tenant" Right="FullControl" /> <AppPermissionRequest Scope="http://sharepoint/taxonomy" Right="Write" /> </AppPermissionRequests>` Helpful information for customizing the AppID permission Request XML

Microsoft: How to create an Office 365 AppID
Permission Request XML (Tenant wide permissions)
<AppPermissionRequests AllowAppOnlyPolicy="true"> <AppPermissionRequest Scope="http://sharepoint/content/tenant" Right="FullControl" /> <AppPermissionRequest Scope="http://sharepoint/taxonomy" Right="Write" /> </AppPermissionRequests>
Helpful information for customizing the AppID permission Request XML

**If you get 401 - Forbidden You may need to run this code and wait 60 minutes.
Set-SPOTenant -DisableCustomAppAuthentication $false
or
Set-PnPTenant -DisableCustomAppAuthentication $false