codeiginter encrypt and decrypt producing new value after each refresh

Sir,

I am using codeiginter 3.1.5 in MAMP Pro.

I have used encrypt library to encrypt the data and send in the url.

When I try to decrypt is not decrypting to the actual value. Each time when I refresh it gives new value because of this I can't get the original value.

encrypt value - wpK8mhnVpEhfc1rv9aDq6A==
decrypt - <<nothing>>

actual value = 1

please help me I tried a lot forums to find the solution.