Set up a standard VM payment, for example a cash on delivery, to see if it goes to the thank You page.
If that does not work
1. Check console for jscript error.
2. Turn on full error reporting
3. Turn on debug in VM
4. Turn on debug in Joomla
Take it one step at a time, do not turn on more than necessary if You find any errors. If no errors found turn on next level.
Jörgen @ Kreativ Fotografi