One of my mums contacts only sends green bubbles
When my mum sends messages to my sister it only sends via text message (green bubbles) and not blue bubbles despite both my mum and sister having iPhone devices. On my mums phone every contact she messages works normally with green bubbles but not my sister.
I did read online that apparently both people have to have imessage enabled but this makes zero sense because when my mum goes out to the shops, I can message her via wifi to her phone and it comes up blue bubbles. Does anyone know what the issue could be?
She also can't send any photos to my sister, it fails to send.
iPhone XR
