Hi Mike,
You need to clarify - are you sending via the Internet or via SMS?
As you say that you can send via a WiFi gateway set up by your son, I am reading between the lines that you are visiting Germany and out on a summit. What Cell-data capability do you have on your phone?
We do not have CDMA or 3G anymore in Germany. Your phone needs to support 4G(LTE) or 5G, your phone contract needs to have roaming data in Germany enabled (and charged for). If you are in a regional area for LTE/4G you are likely to be in an area where only Band 20 (850MHz) is available for data transfer and only Europe-specific cell phones support band 20. Worldwide 1850MHz is used more often (as it is in large cities in Germany).
The simple way to check that you have a working internet data connection to your phone is - is SOTA Spotter displaying new spots? can you send and receive emails? Can you go to a website via the phone’s browser? If not, you have no Internet connection.
The fallback “might” be to use SMS to an in-range 2G Cell tower - that is not always the case, however.
In SOTA spotter your selected SMS gateway is shown in small text to the right of the buttons where you can select Internet Connection or SMS gateway. On that SMS gateway, you need to be authorised - either your telephone number needs to be registered there or your account & password. The best option is to use the sam SMS gateway that you have used before from home.
My suspicion is an incompatibility between your Cell phone and the European cell Networks or your contract simply does not allow you to roam with data outside of the US.
73 Ed.