@Marvin_S What do you think is the best tp-link modem that I can buy with full compatibility for VoIP?

Advanced - Telephony - Telephone Numbers - Modify - Advanced, here i can't find the preferred codec to set for my VoIP, where I could choose between G.711, G.722 etc... I have always found these...

@terziyski thank you, I hope to solve the problem as soon as possible

@terziyski I have this error: Error Code: 85048 Invalid gateway address. Gateway address must be in the same subnet as the network and the host number cannot be binary values of all 0 or 1.

@TPint my internet provider has already activated multicast remotely, he told me that it will almost certainly not be necessary to activate it from the tp-link modem, but he is not sure about this....

@TPint I have Archer VR1200v and not Archer VR1200. I see that modems are very different, like VOIP, one has it, the other doesn't. For VR1200v the last firmware is "Archer_VR1200v(SP)v1_1.0.0 0.8.0...