Was using the default command as * but our extension scheme overlapped with some of the feature codes. Now I have it set to *#[ext] I can do an attended transfer but cannot do a blind transfer.
Blind transfer is already ## so astrix sees ##*# and does not like that scheme?
If your phone has a Transfer button or softkey, try that instead of the DTMF feature code. For example, on Yealink or Grandstream, you would do a blind transfer by pressing the Transfer key, pressing *ext and pressing Transfer again.