Substring is not working in message mapping

Hi All
while am doing the mapping am not able to get the exact value from substring and also when it is blank it is failing . can you let me know what is the wrong am doing here?

"2019-04-24 12:52:30" -- substring - starts with 0 to 10 for field map with A and substring -starts with 12 to 19 for field map with B.

Regards,

Vij