Android Question Print to Bluetooth Printer

FIGURED IT OUT

OK - It may be that there are other issues for bluetooth printing, I don't know, but in my case the problem is with the HP OfficeJet Pro 250 mobile printer itself.

WARNING - do not buy this "Bluetooth" printer for the Bluetooth connection.
( it may be a great mobile printer for other reasons - but don't buy it for the Bluetooth )

Apparently this has a special Low Energy BLE Bluetooth that doesn't really support printing.
Here's the quote from HP's web site. "The BLE feature on the printer is used only to help your Android device find and connect to the printer via Wi-Fi Direct or a Wi-Fi network. . . . . It does not support printing directly over a Bluetooth connection."

That was a few hours of fun finding that out.

By the way while trying to solve my problem I found a nifty printer app called "Print Hammermill" from Aftograf which has very high ratings and claims to support both Bluetooth and WiFi printers from wide variety of manufacturers so you don't need separate apps for each printer.