The CustomerID parameter is documented in the «AlphaHPP» → «Paypage Request Reference» → «Request a Paypage Session» table:
The documentation says:
A customer identifier assigned by the merchant
It is unclear for me, whether the values should be unique or not.
I have got a response from the AlphaCommerceHub support:
CustomerIDis an optional field that can be reported on if required by the merchant.
It can be used to pass information too and from the page, but it’s not really used much past that.
I would recommend ignoring this field and focusing on including any key information in theMerchantTxnID.