I have just installed this package to use the 2 stage Google authentication so great work !
I found a slight issue with generating QR codes.
The output for google two stage authentication formatted URI should be :
otpauth://totp/Example:alice@google.com?secret=JBSWY3DPEHPK3PXP&issuer=Example
the output of your varchar2 missing &issuer.
Simply adding this to the output string will fix the issue.