The logs show audio being sent to flowroute at the address to which they have told you to send it. They show no audio arriving from Flowroute. The fault appears to lie outside of Asterisk.
Flowroute says (lines 374 and 376) send audio, as RTP, using, in decreasing order of preference, µ-law, G.729, and A-law codecs), and RFC 4733 DTMF, to port 28740, on 207.223.67.137.
c=IN IP4 207.223.67.137
m=audio 28740 RTP/AVP 0 18 8 101
You reply (lines 478 and 480) that you want them to send audio to you, as RTP, using µ-law for audio, and RFC 4733 for DTMF, at port number 16304 on AsteriskPubIPaddr
c=IN IP4 AsteriskPubIPaddr
m=audio 16304 RTP/AVP 0 101
You actually send audio to them at the port and address they gave:
20:22:20.868999 IP (tos 0x0, ttl 64, id 4426, offset 0, flags [DF], proto UDP (17), length 200)
p7-1456c.16304 > 207.223.67.137.28740: UDP, length 172
They send no media to you but they have sent an ACK (line 709), confirming that their received the address to which you want media sent:
`ACK sip:AsteriskPrvIPaddr:5060 SIP/2.0`