Pixel xl phone not sending messages to Samsung Galaxy s7

So I just switched from and iPhone 5c to a Pixel xl. I transferred all my data and put in my SIM card. I'm able to message my friends with an iPhone 6 and an Alcetal (??). I tried to message my other friend with a Samsung Galaxy s7 but it didn't appear on their phone. I also used the Samsung to message my new Pixel but it didn't appear on my phone either. I need help with solving this problem. Does anyone have an answer to fixing it? Thanks.

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