Peplink Connection Issues

I have a customer with Peplink using Starlink and is complaining that the connection is slow and not all traffic going through my firewall . I can see traffic coming in and also tested with a laptop showing significant speed. But when my internet is connected to their Peplink, there seems to be issues with slowness and dropouts? Is there any special configuration required from my end or is there any compatibility issue between the two?

Just to clarify that when using only Starkink on their PEPlink there are no issues. But when plugging in my cable as another internet source they experience slowness and dropouts.

Appreciate your feedbacks. TIA :)