Have you read the documentation on tokens? "{number}" is not a valid token. Adding curly braces around a variable name does not make it a token.
The loop will iterate because the token parser strips the braces, and the remaining text ("number") happens to be a valid integer variable name, so that's the action coincidentally working despite the invalid input.
Assuming you want the command to sequentially paste each number:
To have the loop do the counting for you, you'll likely want to use the "Range (For Loop)" option, so you can get the output from the indexer variable to paste (or type)
For that you'll need to add the amount you want to count up by to the starting number, to use as the second parameter (in the "To" field)
E.G.
Get Integer Input [starting]
Get Integer Input [number]
Set integer [target] value to the value of [starting]
Set integer [target] to [target] plus [number]
Start Loop : Repeat From [starting] to [target], using indexer [output]
Set Windows clipboard to '{INT:output}'
Press Left Ctrl+V keys and hold for 0,01 seconds and release
Press Enter key and hold for 0,01 seconds and release
End Loop