Did not receive my 6th drink free (again)

Yesterday, I purchased my 5th drink using the QR code. I even took a picture of the code showing I only needed one more drink purchase before receiving the 6th free. Well today, all my credits are gone and I did not receive my free drink. This is the second time this has happened to me.
To the developers: how do I redeem my free drink?

Zanlund about McDonald's, v5.2.2