clickatell sms "Recipient phone number is invalid or recipient does not want to receive SMS"
Looks like sites/all/modules/civicrm/CRM/Activity/BAO/Activity.php is failing in function function sendSMSMessage( because $doNotSms = TRUE; on line 3154. Set it to false and you should be Ok. However, the check will not happen, so all numbers (even Do Not SMS #s) will get the SMS.

The other option is to comment out the following block and add an if block: 
/*
    if ($smsProviderParams['To']) {
      // If phone number is specified use it
      $toPhoneNumber = trim($smsProviderParams['To']);
      Civi::log()-&gt;debug(print_r($smsProviderParams, true)."\ntoID: $toID\n");
      //echo "&lt;pre&gt;".print_r($smsProviderParams, true)."&lt;/pre&gt;";
      $doNotSms = FALSE;
    }
    elseif ($toID) {
*/
    if ($toID) {
      // No phone number specified, so find a suitable one for the contact