ESP-AT - BT CLASSIC and max SPP connections

[Boscfab]

Hello,
I am using ESP-AT IDF V4.4.2 and have recompiled by enabling BT CLASSIC support.
BT CLASSIC MODE: using an ESP32-WROOM as SPP MASTER, how many ESP32 SPP SLAVE can connect at the same time?
Using the command "AT+BTSPPCONN=<conn_index>, <sec_mode>, <remote_address>", if I set <conn_index> other than "0" I can't connect any device, and I can't connect more than one device at the same time.
Can anyone help me ?
Thanks for your attention,
Fabio