Roaming and can't make calls

You’ll want to start by checking your Self-Serve account to add International Voice Roaming, which is free, and any data roaming add-ons you might need. Wait fifteen minutes and then restart your phone. Turn on Data Roaming in your settings and manually select a partner network like Vodafone or TIM. Set your network to automatic and enable VoLTE. If that fails, try resetting your network settings or testing your SIM in another device. Make sure the date and time are set to local Europe and check for call barring. What phone model are you using? Are you also on prepaid?

I already have a 30 day roaming pass and have been using it. I just all of a sudden can't make outgoing calls

Do you find any of the other features are no longer working or is it just calling? Do you find it’s only in certain areas that it does not work? As it may be the European carriers coverage is just poor in that spot.

Restart your phone and check for network coverage in your area. You can just also manually select a roaming partner network by going to Settings, Mobile Networks, and then Network Operators to pick one. Make sure to set it back to automatic afterward.