YanoSec / Code
Hand grouping from RFC 4648 and RFC 3986.
A six-bit group is a sextet. Regroup into eight-bit bytes after decoding.

Worked bytes: 68 69
UTF-8 letters: hi
Standard Base64 of those bytes: aGk=
The final = is padding. It is not a third letter of hi.

URI percent-encoding: %20 is the octet 20 hex, which is a space in US-ASCII.
That is a URI rule. It is not a rule for every form body.

Activity input: b2s=
Operation name: standard Base64 decode. This is not decryption.
b is 011011, 2 is 110110, s is 101100
Regrouped bytes: 01101111 01101011
Hex: 6f 6b
UTF-8 letters: ok
Record the input, the named operation, and the recovered bytes.