When a SIM card is replaced, messages are no longer sent and a mysterious “Error 50” appears on the Xiaomi smartphone screen, it can upset any user, usually at the most inopportune time when you need to urgently confirm your login to a banking application or send an authorization code. The problem is systemic and often due to the fact that MIUI software does not have time to properly update the configuration files of the operator for the new SIM.
Unlike standard network failures, this error code indicates a specific failure to transmit data through the message gateway, which requires a specific approach to diagnosis. A simple reboot of the device here may not help, since the phone may have stored old message center settings of the previous cardholder or outdated network settings. You will need to perform a series of technical manipulations to force the connection profile to be updated.
In this article, we will discuss in detail the algorithms for troubleshooting it on Xiaomi brand devices, taking into account the features of the HyperOS shell and earlier versions of MIUI. We will not rely on random tips, but use proven methods for resetting network settings and manual adjustment of APN parameters, which are guaranteed to solve the problem in 95% of cases.
The nature of the error 50 in the network Megaphone
The 50 error code in a mobile context is often interpreted as “Requested facility not subscribed” or “User not allowed” in the case of a SIM replacement, the Android system on a smartphone may “remember” the old status of services or try to use the incorrect message center address (SMSC), which was relevant to the previous chip or tariff plan.
The MIUI operating system is characterized by aggressive energy saving and tight control of background processes. Once the old SIM card is removed and a new one is installed, the background services responsible for delivering messages may not receive a signal to change profile, which leads to the phone trying to send a message through a “locked” or “non-existent” communication channel for the new card.
⚠️ Note: Error 50 may also occur if the new SIM card temporarily blocks the data service or SMS sent by the operator (for example, due to debt or suspicious activity.
It is important to understand that the problem lies not in the physical damage to the chip, but in the logical conflict between the settings of the handset (phone) and the parameters that the Megafon base station broadcasts. The smartphone receives from the network a command “denied” with the code 50, because the request is formed incorrectly from the point of view of current registration in the network.
Primary Diagnosis and Physical Status Check of SIM
Before we go into the complex menu settings, we need to rule out the trivial physical reasons. SIM card replacement is a mechanical effect on the tray and contacts. If the chip is not installed tightly or contacts are contaminated, the phone can read the card with errors, which leads to a failure of registration in the network and, as a result, an error in sending.
Remove the SIM card tray with a paper clip and carefully examine the gold contacts on the Megafon card itself. They should be free of oxides, grease or dust. Wipe them with soft dry cloth. Also check if the size of the chip matches the size of your Xiaomi tray (usually the Nano-SIM format). Using adapters or cards hand-carved with scissors often leads to unstable contact.
- 📱 Proper installation: Make sure the SIM card lies in the tray straight, does not hang around and protrudes beyond the edges.
- 🔄 Slot change: If your smartphone has two slots, try moving the card from SIM 1st SIM 2.Sometimes the problem lies in the malfunction of a particular reading module.
- 📶 Checking in another device: The most reliable way is to insert a new SIM card into another phone. If the error 50 persists, the problem is exactly on the operator's side or the card itself.
After you re-install the map, wait until the network is fully loaded. The 4G or LTE indicator should burn steadily. If the network icon is constantly lost or changed to E/G, this is a signal of poor contact or chip damage.
Resetting the APN access point settings for MegaFon
The most effective software solution for Xiaomi is to reset the access point settings (APN). Although APN is primarily responsible for mobile Internet, it is through these profiles that the parameters for MMS and service messages are often prescribed. After replacing the SIM card, the old profile can conflict with the new one.
To do this, go to the settings menu. The path may vary slightly depending on the version of MIUI, but the general logic remains the same. You need to find the section responsible for mobile networks. Be careful when entering data if you decide to create a point manually, but you better use the reset function.
The sequence of actions is as follows:
- Open Settings and select a paragraph SIM-maps and mobile networks.
- Select the Megafon SIM card that has the problem.
- Find the Access Point (APN) section.
- In the upper right corner, click on the menu (three dots) and select Reset or Reset to the original.
⚠️ Attention: After discharge APN You have to restart your smartphone. Without a reboot, the new settings may not be fully implemented by the system.
If the automatic reset didn't work, you can create a point manually. Click "New Access Point" and enter the following data relevant to Megafon:
| Parameter | Meaning | Note |
|---|---|---|
| Name. | Megafon Internet | Arbitrary |
| APN | internet | Strictly lowercase |
| Type APN | default,supl,mms | No gaps. |
| Protocol | IPv4/IPv6 | Recommended |
After saving, remember to tick the dot against the created dot to activate it. Some versions of MIUI also require manually specifying MCC and MNC (country and operator code), but usually they are pulled up automatically from the SIM card.
💡
If after resetting the APN, the Internet worked, and SMS is still not sent, the problem lies in the settings of the message center, not in the access point.
Configure and verify the message center number (SMSC)
The key element in the SMS delivery chain is the message center number (SMSC). If this field has the wrong number or it is empty, the message will not leave and you will receive a delivery error. OTA-This is a customization, but on Xiaomi this process sometimes fails.
You can check and change the message center number through the standard Messages app, but in newer versions of Android and MIUI, access to this field is often hidden. Try the following way: open the Messages app, click three dots in the corner, select Settings, then Additional (or Service Messages) and find Message Center.
For a Megafon SIM card, the message center number must be as follows:
+79269990123If you see a different number or character set, replace it with the one above. In some cases, the field may be blocked for editing. Then the following trick will help: insert the SIM card into a button phone (for example, an old Nokia or Alcatel), where the menu is simpler, enter the center number manually there, save, and re-translate the map to Xiaomi.
- ✅ Number format: Make sure the number is recorded in an international format (via the number number number number number) +7), not in the internal (after 8).
- 📝 Extra symbols: There should be no letters, brackets or dashes in the field, only numbers and plus sign.
- 🔄 Update: After changing the number, be sure to turn off and turn on the “On the plane” mode for re-registration on the network.
Specific MIUI settings and Messages applications
The MIUI shell is known for its rigid limitations on application background activity.The system can block the message service from functioning as "heavy" or malicious, especially immediately after system events such as SIM replacement.This often leads to a connection timeout and a 50 error.
You need to check the permissions and battery settings for the Messages app. Go to Settings → Apps → All apps. Find Messages (or Mi Messages if you use the standard one) Go to Activity Control (or Energy Saving) and select No Limits mode, which will allow the app to run in the background without interruption.
☑️ Checking settings MIUI
Also, it is worth clearing the cache of the message app. Accumulated temporary files may contain erroneous data about the previous SIM card. In the app menu, click Storage → Clear cache. Don't worry, your text messages will not be deleted, only temporary service files will be cleared.
If you use a third-party SMS app (like Google Messages or Textra), make sure it is installed as the default app. Conflict between a standard Mi Messages and a third-party client can also cause crashes when sending. You can switch to the phone settings for Default App → SMS.
⚠️ Attention: In new versions MIUI (13, 14, HyperOS) has implemented spam protection, check if sending messages to short numbers in the security settings is accidentally blocked.
Radical measures: Resetting network settings
If none of the above methods helped fix error 50, the last software method before contacting the salon is a complete reset of network settings, which will return all parameters of Wi-Fi, Bluetooth and mobile networks to factory values.
Important: This operation will delete all saved passwords from Wi-Fi networks and other Bluetooth devices, but your personal files, photos and contacts will remain intact. This is a safe procedure for user data, but takes time to reconfigure the connections.
Perform reset by the following algorithm:
- Open the smartphone settings.
- Go to Connect and Sharing (or Additional Features in older versions).
- Find Reset Wi-Fi, mobile networks and Bluetooth.
- Click the Reset button and confirm the action with the unlock password of the screen.
Once rebooted, the phone will start to register again on the Megafon network, which can take up to 5-10 minutes, during which time the phone may lose signal several times, wait for the stable 4G icon to appear, and try sending a test SMS.