If your free trial hasn't expired or you’ve upgraded to a paid plan, your QR Codes are scannable. If your codes aren't working it’s most likely due to significant design changes since certain apps have more difficulty scanning complex QR Codes.
In terms of design, note that the code's background and foreground colors should have sufficient contrast and the background shouldn’t be darker than the foreground (e.g. a white QR Code on a black background won't be readable by all scanners).
Also, the QR Code should be printed in the appropriate size. We recommend a minimum size of 2 x 2 cm for Dynamic Codes and 3 x 3 cm for Static Codes. Lastly, logos shouldn’t obstruct important elements of the Code.
Find more tips and tricks in Successful Design of QR Codes.