Step1: You MUST connect pen tablets to your iPhone via Bluetooth.
Step2: Open ibisPaint and click "setting" button in the upper right corner.
Step3: On the pop-up, slip down to Pressure Sensitive Stylus to choose HUION Pen Tablet.
Step4: Now you can draw in ibisPaint.
Note: Please use your iPhone horizontally as this time we map the work area of your iPhone to the whole work area of the pen tablets which is completely different from the directions in Android( we use phones vertically in Android while it takes up the left part of work area of pen tablet )
You can also refer to the following articles that will help you use ibisPaint better with our pen tablet.
Which models can support iOS/iPadOS by using ibisPaint
How to set pen pressure in ibisPaint in iOS/iPadOS
How to set shortcuts in ibisPaint in iOS/iPadOS