3CX responded to BYE message with "415 Unsupported Media Type".

[YahyaFlaifel]

3CX responded to BYE message with "415 Unsupported Media Type", this makes call stuck on system and reserve all available channels.

 

[cobaltit]

Which 3CX certified trunking provider are you using? Is your system passing the firewall test?

 

[YiannisH_3CX]

Also without looking in the SIP messages we cannot determine what is causing the issue. From your screenshot we cannot even be sure what devices are involved and it would help if you could describe the call flow. Where is call going?
Can you also provide the information described here: https://www.3cx.com/community/threads/information-to-provide-when-requesting-help.67558/