Update Site Sharing Capability with Flow > How to use "admin.sp.com/_api/Tenant/Sites/Update"

In case someone looking for a solution, this is how I manage to solve this:

you need to use admin API, the URL of the admin API is 

https://{tenant name}-admin.sharepoint.com/

you will need the site ID of the site that you want to change the sharing setting.

in your power automate add a new 'Send HTTP request to SharePoint'

Site address: https://{tenant name}-admin.sharepoint.com/

Method: Post

Uri: _api/Microsoft.Online.SharePoint.TenantAdministration.Tenant/Sites('{Site ID}')

Headers:

• accept  :   application/json;odata=verbose
• content-type:    application/json;odata=verbose
• X-HTTP-Method:     MERGE

Body:

{
"__metadata": {
"type": "Microsoft.Online.SharePoint.TenantAdministration.SiteProperties"
},
"SharingCapability": 1
}