[Bash] 'sleep' x becomes 'leep' x

Hello,

I just started to write small scripts for my Kobo Mini.
At some points I need the script to pause for a few seconds.
So I used the sleep command.
Unfortunately the scripts don't work as they should.
After every 'sleep' command I get the error: 'leep: invalid number '
Independent of the number I use.
So 'sleep 2' --> 'leep: invalid number '
'sleep 10' --> 'leep: invalid number '

Any ideas how I can solve this Problem or another way to pause a script for a few seconds?

Thanks :)