Hi,
can you maintain the following values in the catalog call in SRM (SPRO):
BYPASS_OUTB_HANDLER X
BYPASS_INB_HANDLER X
When you call an external catalog without these parameters first a call is made from SRM to SRM to create an iframe and then the external catalog is called from that iframe, maybe this interferes with the reverse proxy.
When you bypass this, the external catalog should open directly without any calls to SRM first.
Also take a look at the following document:
It might help .
Regards,
Robin