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Hi Dave

The guide you used to install with is old, its was for debian 6 you are probably using 9 (Stretch) though most of it is probably still valid. The entery for wpa.conf should be in /etc/wpa_supplicant/wpa_supplicant.conf and is most probably already there as you have had network working. Also the entry in /etc/network/interfaces is not used in stretch either. But as long as you cleared that out while following the guide then thats fine.

I presume the USB Wifi is capable of using and access point, confirm with entering in a terminal window; iw dev and you should see a line with "Supported interface modes:" and look for * AP.

I think the issue is the TP-Link_TL-WN722N uses the RTL8188EUS chipset which unfortunately is not compatible with hostapd which manages the hotspot. There is an alternative version that is available on github that you can try, in theory it should be fine but it is not tested. Search for hostapd with RTL8188 , https://github.com/jenssegers/RTL8188-hostapd

Otherwise you will need to use the internal wifi for the access point.