Problems with texting after switching from android to iphone

I just got the iphone 12 pro and switched from pixel 3. When I try to text people who don't have iphones I get a message that says "number not available. which number would you like to send the message with?". It only allows me to click primary or cancel. If I click primary, it will send the text but then somehow I get the text on the android even though it's not registering the old sim card anymore. How do I fix this?