How to get exact value from url in php CI?

I try to get encrypted value from url request in PHP CI

Link example = abc.com/?txTd=369gx4NCCyF+eV3YE0veng==

When i try to get txTd, the output is different

$book_id = $_GET[‘txTd’]; the the result is 369gx4NCCyF eV3YE0veng==

+ is missing from the string. Is there anyway to get exact url ? or the encryption key should be change ?

EDIT
I try to put every symbol in the txTd. and the result is if there are #& in the middle of the value , the rest of value will not be shown, and also if there is + , + will change to space. So is there any way to encrypt without #&+ symbols?