That the problem with allopass...there is no "documentation" and the given information are in french within their website!!
here is their "hello" script to get familliar with allopass(not totally accurate with AEC) http://www.allopass.com/dnl/AP_gallery_select.txt

here is my doc to you

in allopass administration you have to give 3 URLs
-error url( where client will be redirect if wrong code given)
-acces url(where the allopass form should appear =where the user enter his code)
-doc url(where the protected doc remain on site and where client will be redirect if a good code is given  for us it will be something like this
http://www.mysite.tld/index.php?option=com_acctexp&task=allopassnotification)


here is the minmum required to use allopass gateway:
A)fields
IDS :SITE_ID (given within allopass account.. in our case its a $cfg parameter)
IDD :DOC_ID  (given within allopass account.. in our case its a $cfg parameter)
code[]:user

Abis)optional field
DATA (type hidden) :these value will be return  attach at the end of the "doc url"  so we can put here information like invoice number
RECALL:if set to 1 , the CODE will be return  attach at the end of the "doc url"

B)user information
a png image within allopass website wich give information to user on how to use allopass gateway(basically a paying vocal server which generate a valid random code on each call)
 in our case:
http://payment.allopass.com/acte/scripts/popup/access.apu?ids=165776&idd=455780⟨=fr&country=fr

C)post url (where the allopass magic happen) :
 http://payment.allopass.com/acte/access.apu


here is their given  example:
http://www.allopass.com/webm_script.php4?SITE_ID=165776&DOC_ID=455780&LG_SCRIPT=fr_uk&TYPE_SCRIPT=iframe&APERCU=1

they also give a way for develloper to  integrate allopass and test the user given code against their plateform:

http://www.allopass.com/check/index.php4?CODE=$code&SITE_ID=$siteid&DOC_ID=$docid
or
http://payment.allopass.com/api/checkcode.apu?code=$CODE&auth=$AUTH

with  $auth = AUTH (given within allopass account.. in our case its a $cfg parameter)

three kind of answer from the server :
OK (code correct)
NOK (code invalid)
ERR (invalid request)



hope it would help
feel free to ask for more information

 to get help on AEC:

http://www.globalnerd.org