Message Card Action Buttons not working consistently

Thank you for your answer, Meghana-MSFT.

Sure, please find the JSON below:

{
  "@context": "https://schema.org/extensions",
  "@type": "MessageCard",
  "themeColor": "FFB900",
  "title": "Missed call from <PHONE_NUMBER>",
  "text": "Name: <CALLER_NAME>, Mobil [Shared Mailbox]<br>  Voice Apps: Voice App 1, Voice App 2 <br> Date: 27.07.2023 <br> Time: 10:10 ",
  "potentialAction": [
    {
      "@type": "OpenUri",
      "name": "Call <PHONE_NUMBER>",
      "targets": [
        {
          "os": "default",
          "uri": "https://teams.microsoft.com/l/call/0/0?users=<PHONE_NUMBER>"
        }
      ]
    },
    {
      "@type": "HttpPOST",
      "name": "Task completed",
      "target": "<APP_URI>/<ACTION>?code=<TOKEN_CODE>",
      "body": "{\r\n \"Number\": \"<PHONE_NUMBER>\", \"messageCardDate\": \"27.07.2023\", \"messageCardTime\": \"10:10\", \"localTimeZone\": \"W. Europe Standard Time\", \"callerLookupName\": \"<CALLER_NAME>, Mobil\",  \"language\": \"ger\", \"voiceAppName\": \"Voice App 1, Voice App 2\"\r\n}",
      "headers": [
        {
          "Content-Type": "application/json"
        }
      ]
    }
  ]
}