Hello ＋Xfreezer ,

What you could try first is to clear the browser cache.  
If you use Safari, go to Settings -> Safari, scroll down a bit then tap onto "Clear History and Website Data".

If you use another browser, please google for detailed information. 

Something else you can try is to hold your square, and check whether you are able to write now. :)) 

And last but not least you could do a "soft reset" of your iPhone.  
A soft reset forcefully power-cycles the iPhone and clears all memory. By doing so, you won't lose any data, and you won't wipe the device. I'ts a safe procedure.

To do a soft reset, press and quickly release the volume + button, then press and quickly release the volume -  button. Then press AND HOLD the side button .. .. when the Apple logo appears, release the side button. 


Kind regards,
John :)