what settings need to be changed from API2 to AP!2 modes

I am able to communicate between a coordinator and two routers using API2, but have run into some difficulties which is some circumstances a single packet transmission by 64 bit address from the coordinator to one router causes the other XBee router to start an endless stream of packet transmissions. The Knowledge base that I have just read suggests that I should not be using API2 but should use API1. I have tried resetting all three XBees to API1 by changing the AP setting. On doing so the coordinator can receive messages from the routers, but the routers no longer receive from the coordinator.
Are there any other settings that need to be changed to make API1 work?
Do you have any thoughts on the problem in API2 mode?

Both API modes are 99% similar. Its just that in API2 mode, couple of Hex values are escaped (flagged) so they do not interfere with the data frame sequencing.

You need not change any other setting for API1 operation. Cross check that all modules are in API1 mode and Tx API frames are also designed in API1 format (use XCTU frame generator for convenience).

If this goes well, then only thing left is to check if address has been done properly in API frame itself.