Update #1: I updated the models to work better with the new method, and add new stand model.

I tried to make the description and the solution in such a way that it could be done easily, without  special program, and knowledge.

Color printing is easy with Z layer height change.

The model is similar in width and rounding to the spotify code models found here: https://www.prusaprinters.org/prints/62809-spotify-code-wall-ornament-with-custom-code , and they look good together.

New Method:

Required PrusaSlicer 2.7.0-alpha1 or later
A thousand thanks to Prusa Team and Community that since 2.7 version we can easily use svgs in the slicer as modifiers, negative volume, etc., a very useful function.

Generate QR Code

1. Open this page : https://observablehq.com/@johnboiles/wifi-qr-code-svg-generator
2. Enter the ssid of your wifi network, and password.
3. Select the type of encryption and whether the network is hidden.
4. Inset from the cutout path and the QR code : 0 mm
5. Make sure that the generated qr code is working properly.
6. Download the Svg file.

Preparing for 3D printing.

1. Open PrusaSlicer of course.=)
2. Select the base model you want, depending on whether you want to create it in two or three colors and with text.
3. Right-click the base model. Add Negativ Volume → Load and select the Downloaded SVG
4. SVG Settings: 
   1. Depth: 1.0mm 
   2. Use surface: Yes
5. Set the desired size and position of the qr code on the model.
6. Slice it up with the colors and settings you need.
7. Once again, make sure you that working QR code.
8. And that's all, Happy Printing. =)

Old Method:

//Generate QR Code

1. Open this page : https://observablehq.com/@johnboiles/wifi-qr-code-svg-generator
2. Enter the ssid of your wifi network, and password.
3. Select the type of encryption and whether the network is hidden.
4. You do not need to modify other settings.
5. Make sure that the generated qr code is working properly.
6. Download the Svg file.

Code model preparation for Tinkercad

1. Login, or registration on the free Tinkercad at www.tinkercad.com
2. Import the Svg file.
3. Don't modify the Scale
4. You'll see a big cube with the code in it, you don't have to do anything with it, just export it.
5. Export the file in Stl format

Preparing for 3D printing.

1. Open PrusaSlicer of course.=)
2. Select the base model you want, depending on whether you want to create it in two or three colors and with text.
3. Right-click the base model. Add Part → Load and select the QR Code Stl file previously downloaded from the Tinkercad.
4. First, repair the model with the Netfabb.
5. Once the file is displayed it will not be the correct size, but this can be easily modified
6. Select the added stlt file from the drop-down on the right side of the main file
7. Then open the small padlock on the part manipulation tab and set the Z Size of the added model to 3mm. X and Y size to 100mm.
8. Click the apperas small icon on the right (Drop to Bed)
9. Slice it up with the colors and settings you need.
10. Once again, make sure you that working QR code.
11. Happy Printing. =)//

Print Settings

• Nozzle: 0.4mm
• Layerheight: 0.20mm
• For a nicer pattern: Change the Lift Z to 0.1
• Detect thin walls: On