Ad-Hoc Entra MFA using SMS

Error : 

Get MFA Client Access TokenDone.
Send MFA challenge to the user
Done.

OTP sent to your phone. Please enter the OTP:
                                                  Enter the OTP sent via SMS: 696632
Invoke-RestMethod: C:\Git_Repo\MFA_Test\MFATestWIthKyle\sms.ps1:54:28
Line |
  54 |  … ionResult = Invoke-RestMethod -Uri 'https://strongauthenticationservi …
     |                ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     |           Service     BODY { color: #000000; background-color: white; font-family: Verdana; margin-left: 0px; margin-top: 0px; 
     | } #content { margin-left: 30px; font-size: .70em; padding-bottom: 2em; } A:link { color: #336699; font-weight: bold;
     | text-decoration: underline; } A:visited { color: #6699cc; font-weight: bold; text-decoration: underline; } A:active { color:    
     | #336699; font-weight: bold; text-decoration: underline; } .heading1 { background-color: #003366; border-bottom: #336699 6px     
     | solid; color: #ffffff; font-family: Tahoma; font-size: 26px; font-weight: normal;margin: 0em 0em 10px -20px; padding-bottom:    
     | 8px; padding-left: 30px;padding-top: 16px;} pre { font-size:small; background-color: #e5e5cc; padding: 5px; font-family:        
     | Courier New; margin-top: 0px; border: 1px #f0f0e0 solid; white-space: pre-wrap; white-space: -pre-wrap; word-wrap: break-word;  
     | } table { border-collapse: collapse; border-spacing: 0px; font-family: Verdana;} table th { border-right: 2px white solid;      
     | border-bottom: 2px white solid; font-weight: bold; background-color: #cecf9c;} table td { border-right: 2px white solid;        
     | border-bottom: 2px white solid; background-color: #e5e5cc;}                  Service       Endpoint not found.
WARNING: Invalid OTP or validation failed.

Below line causing the error 

$mfaValidationResult = Invoke-RestMethod -Uri 'https://strongauthenticationservice.auth.microsoft.com/StrongAuthenticationService.svc/Connector//ValidatePin' -Method POST -Headers $Headers -Body $XML -ContentType 'application/xml'