using dual sim with one us service and one foreign (EU) service when traveling in third countries

Can I get some help understanding how my dual sim card iphone works with a US service ESIM and a physical SIM card from Spain, where I often reside, in the other slot. I am having an awful time when traveling out of either country. In the EU, my Spanish SIM card should work and when it was the only card in an earlier version of my iPhones, it did. But now I don't receive phone calls or texts to that number when out of Spain. And yes, it is "on" for both voice and data. My WhatsAPP , tied to my Spanish cell phone number works fine, however.

Help anyone? I don't inow how to make this work for me....

Melissa