Teezily is the only platform that allow you to sell a print-on-demand product with custom text and image design and it very simple if you follow these steps:
Make a design and leave a blank space anywhere you want to add custom text. Please keep in mind that you have maximum 3 custom text for each design, and you can also upload your font if you want.
When upload your campaign, please insert a text box at the blank space you left, and check the "Set as customizable text".
To offer your buyers the possibility to add a custom image check the following video tutorial :