How come some girls whom I'm following on IG haven't read my messages I sent to them? The word "seen" is not visible even tho I send them 3 messages?

[Justaguy43]

Some girls have read my messages as the word "seen" is written but some girls whom I'm following ( but they aren't following me) haven't read my messages since the word "seen" is not visible. Do they have to follow me back for them to see my messages?

[Screenwriter]

You'll have to ask the site managers to find out what the protocol is. It's according to what level of messaging the person allows. Often if the person doesn't follow you, they don't accept messages from you. In other cases, popular IG people simply don't respond to random messages.