Add a "/#" (a slash and a hashtag) at the end of your URL to make the browser ignore the trailing numbers for custom designs. See [Note 1]
[Note 1] The app generates numerical data to encode the graphic design and adds it after the URL. By adding a "/#" at the end of the URL, before the numbers, the browser treats the numbers as an anchor. Browsers safely ignore anchors that don't exist, so the QR code will point to the URL no matter what design is created.
[Note 2] QR alphanumeric mode supports only A–Z (not a–z). Uppercasing lets more of the URL use the compact 6-bit-per-character alphanumeric encoding instead of 8-bit byte mode, producing a denser or lower-version code.