Help with images not showing up on emails (Mailgun)

Hi,

I need to send emails for a casting app for commercials ( booking talents) but sometimes the images don't appear on the email and become attachments instead.

I tried using sendpulse and now I switched to Mailgun but the problem still occurs.

I believe this only happens when sending to hosted email servers? It works fine on Gmail and testing on Mailtrap.

 "message": {
        "headers": {
            "to": "bookings@-------",
            "message-id": "449fa4602732d6387a4977cbf2ad6f41@-----",
            "from": "Talento <noreply@------->",
            "subject": "Sub list for FLATMATE OPTIONS"
        },
        "attachments": [],
        "size": 855019
    },
    "recipient": "bookings@-----",
    "event": "delivered",
    "delivery-status": {
        "tls": true,
        "mx-host": "aspmx.l.google.com",
        "attempt-no": 1,
        "description": "",
        "session-seconds": 1.37363600730896,
        "code": 250,
        "message": "OK",
        "certificate-verified": true
    }