I have successfully tested X-Payments 1.0.6 with X-Cart 4.5.4
I don't know why it was said that 4.5.5 was REQUIRED to use XP 1.0.6?
There appears to be two APIs (1.1, 1.2) and xc 4.5.4, it uses the "API 1.1 version is supported"
In practical use, there appears to be no difference to the 4.5.4 store to use X-P 1.0.6 (vs. 1.0.5)
I now have 1.0.6/4.5.4 provisioned with an iFrame using Altered Cart's X-Payments Connector For Checkout One
and it's a SIGNIFICANT improvement over the stock code. But that's the subject of a new thread.
Just wanted to let everyone know that it's OK to use 1.0.6 w/ 4.5.4 and if your goal is improved iFrame support using Checkout_One and the C1 connector, this is the way to do it without "upgrading" to 4.5.5
PS -- if you start using a new XP version, make certain you run cleanup.php on your 4.5.4 store before you run a test transaction. (I didn't and received 403 errors on the transaction callback - after running cleanup.php, everything is perfect!)