Good evening. I have integrated Gas Engineer Software with yourselves, but the invoice that has been sent and subsequently paid has not shown up on the app or online

Hello there, @userchandleyph.

QuickBooks Online (QBO) works with multiple applications as long as it's listed and available on the app center. Let's verify if the Gas Engineer Software integrates with QBO. If not, I recommend reaching out to the app provider and request them to contact our Developer Team to initiate a connection between the application and QuickBooks.

Also, feel free to visit our Help articles page for reference. There, you can read some of the helpful articles that'll guide you in your future tasks.

We're always here to help. Your success with QuickBooks is our top priority.

This keeps happening every message I try to send.

I keep getting this when I write a reply to your message. 

Hello there, userchandleyph. I've seen the screenshot you've attached above.

I appreciate you for sharing the error message you're getting here. Have you tried replying here using a private browser? If not yet, let's try it to isolate if the error is caused by having too much data is our browser. Here are the things to do:

1. Click the Reload icon or press F5 on your keyboard. It's a way to refresh your browser from any unexpected behavior you've encountered.
2. If the same thing happens, log in to your QBO account by following these shortcut keys:
   
   Google Chrome: Ctrl + Shift + N
   Microsoft Edge: Ctrl +Shift + P
   Firefox: Ctrl + Shift + P
   Safari: Command + Shift + N
    
3. If you're able to post here without getting an error message,  we can go back to your original browser and clear the cache. 
4. One more thing we can try on is to use other supported browsers like Mozilla, Google Chrome, Microsoft Edge, and Safari. For Safari, make sure to use the latest one. It's important to clear the cache and use these compatible browser to get a better experience when doing some important thing in QuickBooks and other websites.

Please let me know if you still need assistance with this matter. I'm always free to help. Take care and have a good one!