[SR-Users] tls connections

I'm trying in vain to get a tls connection to  a carrier. ~Without too much detail we are exchanging certificates and they are saying we are triggering a reset of the connection because we are requesting to chage the tcp window size. there are requiring us to have a window size of 65535. there we are sending a smaller window size. as far as I understand this should be OK. I have tried to force out linux install to set the window size to 65535 but we are still sing the smallerwindow in the tcp packet. Is there any settings in Kamailio that could force the window size? we are using Kamailio 5.4.2 Thanks in advance Richard