What does it mean when the message appears "OWNER NAME declined a request for dollar amt agreed upon"? I had already accepted the booking, so does this mean they cancelled? (this would've been my first booking)
Pretty certain the client cancelled the booking. I would call or text the potential client to find out why their plans changed. and to thank them for considering using your services
It doesn't look like the cancelled, it looks like you accepted the request but they did not. A booking has to be accepted by both parties. Once one party clicks "book it", the other will get a notification asking them to either "Accept" or "Decline". If they click "accept", then you're booked! If not, you will get a message following the format you mentioned.
Before accepting bookings, make sure you communicate with the owner about what they are looking for, whether they would like to meet prior, etc. If you already did those things prior to clicking "Book It", you could attempt to message the owners to see if their plans changed, like Walt mentioned.