We suspect that there was one possible option for him to be in trouble. That one option is that Onesimus stole something from Philemon, now that may have been money or livestock, we have no record if he did steal something and if he did what he stole. Now there are a few different options for how Onesimus ended up meeting Paul. One of them was that after he fled Philemon he by some chance ran into Paul which is the less likely option. The more likely option seems to be after he made his master mad, he went out to specifically find Paul because he had converted Philemon earlier and hoped to make peace with his master. Paul finds Onesimus to be so useful to both men that he tells Philemon that if Onesimus did steal from him that Paul will pay
