In one case I recently helped troubleshoot, roaming worked normally for the first couple of days overseas and then suddenly stopped.

The phone later received an Optus message saying Daily Roaming could not be added because there was an issue completing the order.

After working through the normal handset-side steps, the eventual fix was for Optus to remove and re-add international roaming to the mobile service.

Before you get to that point, these are the steps worth trying first.

1. Check international roaming is enabled

Open the My Optus app, select the affected mobile number, and check that International Roaming is enabled.

Also check the phone itself.

On an iPhone:

Settings -> Mobile -> Mobile Data Options -> Data Roaming

Make sure Data Roaming is turned on.

On Android, the setting is normally under:

Settings -> Connections / Network & Internet -> Mobile Networks

The exact wording varies between phones.

2. Force the phone to reconnect

Sometimes the phone simply needs to re-register with the overseas mobile network.

Try this sequence:

1. Turn Wi-Fi off.
2. Turn Airplane Mode on for around 10 seconds and then turn it off.
3. Turn Mobile Data off and back on.
4. Turn Data Roaming off and back on.
5. Restart the phone completely.
6. Wait a few minutes for the phone to reconnect to the local network.

It can also help to send a normal SMS to an Australian mobile number or make a short voice call. This may trigger the Daily Roaming service.

If you are using an iPhone, make sure the test message is being sent as an SMS rather than iMessage.

3. Try selecting the overseas network manually

If automatic network selection is not working, try selecting one of the local networks manually.

For example, in Japan the major networks include:

• NTT Docomo
• KDDI (au)
• SoftBank

On an iPhone, look under:

Settings -> Mobile -> Network Selection

Turn Automatic off and wait for the available networks to appear.

Try each available network individually. After selecting one, give the phone a minute or two to register, then try sending an SMS or making a call.

When you have finished testing, you can normally return Network Selection to Automatic.

4. Pay attention to any Optus error message

If you receive a message similar to this:

We couldn't add Optus Daily Roaming to your service because there was an issue completing your order.

that may indicate something different from an ordinary phone connection problem.

The phone may be successfully connecting to an overseas network, but Optus's systems may be having difficulty activating the Daily Roaming add-on.

Possible causes include an incomplete account order, a billing-system problem, or a roaming provisioning issue.

5. Check your billing details

Because Daily Roaming is normally activated and charged automatically, it is worth checking that your payment method is current.

Look for:

• an expired or old card
• failed payments
• pending account changes
• an old payment method that may still be attached to the account

However, a billing-related roaming error does not necessarily mean your bank has declined the card. The issue can also sit within the provider's own ordering or provisioning system.

6. If it previously worked, tell support

This is useful information.

If Daily Roaming worked for several days and then suddenly stopped, tell Optus exactly that.

Also check your account history to see whether earlier Daily Roaming charges were processed successfully. That helps distinguish between a phone that has never roamed successfully and a service that was working but later developed a problem.

7. If all the phone troubleshooting fails, ask Optus to check provisioning

After you have:

• confirmed Data Roaming is enabled
• restarted the phone
• toggled Airplane Mode
• tried SMS and calls
• manually tried available roaming networks
• checked the payment method

and roaming still does not work, it is worth asking Optus to check the service itself rather than repeating only handset troubleshooting.

A useful question is:

In the case that prompted this guide, re-adding roaming to the account was what finally restored the service.

Final tip

Keep screenshots of any roaming error messages and make a note of which troubleshooting steps you have already tried. If the issue needs to be escalated, this can save a lot of repeated troubleshooting.

Roaming involves several different systems: your phone, the overseas network, the Australian carrier's roaming platform, and billing. An apparently simple problem can sometimes take a little investigation to isolate.

The good news is that if your phone was previously roaming successfully, the issue may be something relatively small that can be corrected once the right part of the service is checked.