Which phone are you using, your issue might be the VoLTE issue https://www.koodomobile.com/en/help/3gshutdownUS

As of now, can you connect to any us carrier at all? Have you also tried to reset network settings of the phone to see if it help?

A Samsung and no I can't connect to any, I tried restarting and reseting too. Didn't work.

Have you enabled data roaming on your phone? 

Which add on did you buy though? Was it a US data roaming or voice and text? In your area where you traveling to, were people there having wireless signal? Can you manually select an US carrier in the settings?
As well, which samsung model was it? 

Yes I enabled data roaming. I purchased the data and minute add ons. I'm in Columbus, OH. No I can't manually select a US carrier, there no such setting that I'm aware of in my account. A23

To select another carrier manually, go to settings >> connection >> Mobile network >> network operator >> turn off "select automatically" and manually select a Carriers showing up there.

As you are in the US, there wasn't a Koodo network so I recommend you reset network settings to make sure the phone wasn't fixed to Koodo settings.

I tried it multiple times and it didn't work

I presume that you're prepaid?

Yes

What error did you see and when you said it didn't work, which didn't work? As we are all customer here, and you are overseas, more information and more detail is good to help other understanding your case.

I followed the steps you put down for me, and tried to connect to the carriers available multiple times, but I couldn't connect to them even after turning in it off and on multiple times.

So did you see any carriers in the list? Or it was empty? US carrier doesn't support 3G so your phone must be on a LTE mode as well.

I saw two, and tried connecting two those two, and yes my phone was on LTE mode throughout. 

Is VoLTE on?

DO you even see this setting?

https://deviceguides.vodafone.co.uk/samsung/galaxy-a23-5g-android-12-0/calls-and-contacts/turn-volte-on-or-off/

I said yes. Or did you not see I just said it was turned on the whole time. Also "Dennis" I think you're being rude especially with the second question you asked.

I still do not see you say yes to VoLTE.  I see you say yes to LTE only.  LTE and VoLTE are 2 separate things.

If my comment came across as rude, it was not my intention.  I see the word “Do” as fully capitalized which sounds like I am emphasizing that.  It is purely my slow reacting pinky finger on my shift key.  

I ask if you see VoLTE in your settings because if Koodo does not have VoLTE setup on your prepaid account, then you likely will not see VoLTE as a setting in your phone, hence why I also included a link to find the VoLTE setting.

Then yes, the VoLTE setting is turned on.

How is the roaming now? If it still not working, honestly, I recommend you visit a local US carrier and get a SIM to use. Koodo prepaid roaming has been an issue recently. You can check the link in my first post.

You could try to chat with a rep via Facebook/Twitter messaging and ask them to refund the US booster. Not sure if they can as they might not have access to prepaid system. But you could try. Links to their official Facebook/Twitter are below at the bottom of this forum.

Phones have to be VoLTE compatible to work in the US plus the feature has to be activated on your prepaid account. You need a rep to do this, but you must start with a chat and make sure your hardware will work.
Phones commonly compatible in the US:

https://www.att.com/scmsassets/support/wireless/devices-working-on-att-network.pdf?source=ESSZ0SSPR00T1EsEM&wtExtndSource=20201020164156_AT%26T+Community+Forums__COMMUNITY_3954573197

Chat with Koodo prepaid:

https://widget.telus.tiia.ai/koodoprepaid/koodoprepaid.html