You should stop texting a girl when she does not reply to you.

This doesn’t mean she is not replying when she is justifiably busy but she is not replying because she legitimately is not busy, sees your texts and just doesn’t want to reply.

This could be because she was just using you as an emotional pillow, wasting time due to boredom, trying to have and maintain a transactional relationship or she just lost interest because she found someone else or you said something wrong.
If you text her and you know she is not doing anything, yet you have given her a reasonable amount of time to reply and she doesn’t then that can be a huge clue that you should stop messaging her. You can try another time, such as messaging the next day or day after because she could have been in the middle of something and just forgot to message you. So giving a day or two to reply and then following up with a text would be a great idea. If she doesn’t reply this time then it is legitimized that she does not want to talk to you.

Typically, when a woman starts to slow down with the texts and replies then that already gives you a clue. When she gives you one or two word replies then that is another clue. When you have to message her twice to get a reply then that is one more clue.

Use these clues as red flags that things aren’t going so good and it is best you either try again (one last time), take the interaction offline and meet in person or save your energy and move on.