As for looking for errors, click the arrows above and below the error.
MitAi2 is a free website mainly for learning and simple applications. Don't expect miracles from her. If you want something better, learn Java and create in Android Studio. Otherwise, you have to get used to the limitations of AI2 and know how to handle them.
As for the operations on the texts that you presented above, I will take a look at it and introduce it to my extension as part of learning to write extensions.
ASC (Letter)
CHR (digit)
These functions are provided by my extension. You can convert UTF8 encoded character arrays in it.
For example, the string "hello" will convert to "68656C6C6F" and vice versa. Characters outside the ASCII range, e.g. the pound symbol as "C2A3".
There is a "Trim" function in blocks that removes spaces from both sides. "Rights (Text, Len)" is in blocks "Segment text, start, length".