iMessage waiting for user to accept

I resolved this problem by deleting all the files in this folders

~/Library/Messages

~/Library/Containers/com.apple.iChat/Data/Library/Messages/Archive

and iMessages start to work immediately.

Hope it work for everyone!

Hard core but, if it works, bully for it! For future reference here's how you might be able to get back your messages if you have latest macOS. Enable Messages in iCloud in Messages Accounts settings before you blow away the messages library. Give it time to upload. I think there should be a progress bar at the bottom of the conversations list column. Once it's done or even if it had already been enabled, make absolute sure it's done uploading by clicking on the Sync Now button which should at least momentarily turn to dim, static gray. When it comes back to live black and white, it's done. Now disable Messages in iCloud and give Messages time to communicate that switch to iCloud. Then quit the Messages app (don't just close the UI window), hard-core blow away the messages library per NovaProd's post, open the Messages app and re-enable Messages in iCloud and go from there. Maybe a long shot so, like you said, one should back up the messages they want to keep one way or another before hand.

Exactly the same for me. Been so for a few months. Have used iMessage since it was introduced, so class myself as 'experienced' user. Tried Googlee-ing but mostly obvious suggestions. A work round if you need to send something from your MacBook is to save the file to iCloud drive and then iMessage it from phone or pad. Bit of a bind but works. I keep forgetting that it doesn't work until I see the 'downloading' message, its almost as if some security feature is preventing any files from being sent (via iMessage) out from the macbook, receiving works fine. Let me know if you find a solution, as I will you.

same problem. Used to work. Used to be able to hit the spacebar and see the photo large, too. Then it got stuck on one picture and everytime I hit the spacebar - i only saw that picture no matter which picture i hit the spacebar on. I restarted the computer and now i can't hit the spacebar, download any pictures i receive or send any. It just keeps saying "waiting for (number) to accept in the file transfers. The other person on receives a "downloading" but it never starts downloading on their end. Just says 0 bytes/997kg. (or whatever the size)

I tried a few suggestions from other posts. My IMTransferAgent doesn't show up in utilities activity monitor. I don't know how to open ports. None of that makes sense to me. One cool thing was I figured out how to receive other messages from non iphone users on my messages app. That was cool.

Same issue for weeks now. Won't send images. I get an "cannot be delivered" error. Recipients receive an image icon but it won't download for them. Same when I send them to myself.

I've tried every fix I can find and nothing works.

I also had to reparation my hard drive at one point due to Boot Camp and now I'm having this issue... There might be a correlation here. I'm chatting with an Apple advisor currently and will update with more information.

This is disgusting!!

I'm having this same issue. I've followed all the suggested fixes (baring a clean install) and nothing.

My phone is my business - being unable to send attachments or in some case messages to clients is unacceptable.

Having this exact same problem where I can't send images through iMessage and getting the "Waiting for [recipient] to accept..." under File Transfers. I also have all of the issues of not being able to press space bar to enlarge images from the iMessage window and if it does work it shows the same picture every time that's not the picture I selected. I can email to myself and send images through text on my phone but that's so much work when it used to work properly from my desktop. The only thing I can think of is I just updated to High Sierra 10.13 the other day and this just started happening so thinking it's related.

To troubleshoot I have updated my iPhone and erased the ~/Library/Messages folder with no luck. Didn't see the ~/Library/Containers/com.apple.iChat/Data/Library/Messages/Archive that's listed below. And also didn't see the IMTransferAgent on my Network Activity Monitor. I don't use Boot Camp so thinking there has to be another way than reformatting my whole harddrive.

Hoping someone has something!

Doing what NovaProd said above worked! It got rid of all my messages except for the last one sent/received from each one.

If there is stuff you want to keep from your messages, I suggest going in and saving to your computer before you do this.

This helped me figure out how to get to the library and then messages: http://osxdaily.com/2011/08/31/go-to-folder-useful-mac-os-x-keyboard-shortcut/

This worked for my daughter who was having the same issue. After deleting those files and restarting the messages app, she's able to send images via messages again, though she's still not able to doubleclick on images to view using "quick look".

Thank you NovaProd!

THANK YOU! I can send pictures again. I just can't view them with the spacebar. But thats okay. I can drag them to the desktop and view them.

I copied and pasted what NovaProd wrote in to the spotlight search and it brought me to the right folders.

same problem

there's got to be another way...

have anyone else tried this? or find a fix other than reformatting?

I agree....there has to be another way. I can't find anything online to fix this problem.