Yes, you can't see iPay88 module for PS 1.7 under the download section in iPay88 merchant account, but you can simply request the module by emailing the iPay88 support team.
They will send it to you in email.
I just use the module they send it to me (support PS 1.7).
Perhaps they should just update the download section to include module for PS 1.7 as well by now.