Thanks Bob.
$modx->sendRedirect($url . ' target="_blank" ');
This didn't work but inserting
in the Link attributes and using
$modx->sendRedirect($url,0);
redirects to the remote page and displays in a new page successfully.
I have now used a php function instead of the Redirect in the snippet and it seems to be POSTing the data successfully to the remote site. I just have to wait to see if the other site is able to decode the data correctly.
Hopefully success
Thanks again for your great help.
Have a beer on me