REST API to apply a retention Label

SukeshCrimson here is my JSON code from an HTTP call in Logic apps. It's possible you can perform a similar call in Flow as well, but I haven't tried as there is no direct code edit there.

"Apply_Label": {
	"inputs": {
		"body": {
			"body": "{\n'complianceTag': '@{variables('MyComplianceTagName')}',\n'isTagPolicyHold': 'True',\n'isTagPolicyRecord': 'True'\n}",
			"headers": {
				"Accept": "application/json;odata=verbose",
				"Content-Type": "application/json;odata=verbose"
			},
			"method": "POST",
			"uri": "_api/web/Lists/GetById('@{outputs('Library')}')/items(@{outputs('LocalDocId')})/SetComplianceTag()"
		},
		"host": {
			"connection": {
				"name": "@parameters('$connections')['sharepointonline']['connectionId']"
			}
		},
		"method": "post",
		"path": "/datasets/@{encodeURIComponent(encodeURIComponent(outputs('DocSite')))}/httprequest"
	},
	"runAfter": {
		"XYZ": [
			"Succeeded"
		]
	},
	"type": "ApiConnection"
}

The following is the input interpreted by Logic Apps, including the headers and body:

{
    "method": "post",
    "path": "/datasets/https%253A%252F%252FmyTenant.sharepoint.com%252Fsites%252FmySite/httprequest",
    "host": {
        "connection": {
            "name": "/subscriptions/ffffffff-ffff-ffff-ffff-ffffffffffff/resourceGroups/MyRG/providers/Microsoft.Web/connections/sharepointonline"
        }
    },
    "body": {
        "body": "{\n'complianceTag': 'Exact label name',\n'isTagPolicyHold': 'True',\n'isTagPolicyRecord': 'True'\n}",
        "headers": {
            "Accept": "application/json;odata=verbose",
            "Content-Type": "application/json;odata=verbose"
        },
        "method": "POST",
        "uri": "_api/web/Lists/GetById('xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx')/items(1234)/SetComplianceTag()"
    }
}