My Client cannot connect to audio or video for my call but when they join other Zoom calls it works

[cfyh234]

Hello, when my client (based in UK) joins my (based in South East Asia) call, his mic and video does not work. He is unable to turn on video and/or hear us. We are unable to hear him as well. However, the call works for other people on our team. 

However, when he joins other calls (in Europe), the audio and video function on Zoom works for him. 

May I check if this is a regional issue and if there are any ways we can work around this? 

Thank you!