encryption in php

[MikeSiencyn]

Hi
I am in the process of applying Form Integration to get my website to deal with card payments.
Opayo stipulate the use of encryption using AES (block size 128-bit) in CBC mode with PKCS#5 padding.
I've been trawling through various sites and getting lots of stuff which looks like a possible answer but not quite fitting my situation.
Within my pay.php file I have a variable $preCrypt to which I wish to apply the encryption process the result of which will be declared as the variable $Crypt.
I know what key and initialisation vector to use so I don't need to generate these.
Please could someone give me the php code which will convert $preCrypt into $Crypt.
Opayo also ask me to encode the result in hex (making sure the letters are in upper case).
Many thanks
Mike