Separate the four layers, then run a safe quick check
A phone can show signal bars while having no usable data session. Work through four layers: radio registration, mobile data and an assigned IP, DNS resolution, then the target app. A VPN operates above the base connection and cannot restore a radio or data session that does not exist.
Note whether the display shows 4G, LTE or 5G, whether calls and SMS work, and whether any ordinary site loads. Do not begin by resetting the entire phone.
- Disconnect every VPN, proxy and private DNS override you recognise.
- Confirm mobile data is enabled for the correct SIM.
- Toggle Airplane Mode once, wait, then reconnect.
- Open two ordinary sites by domain name and, if possible, one known IP-based test.
- Restart the phone only after recording the original state.
If no service works, take a screenshot of the signal and network indicator and record the location and time. If only one app fails, keep the network settings intact and diagnose that app separately.
Check the selected SIM, allowance and roaming status
Dual-SIM phones can use one SIM for calls and another for data. Confirm the data SIM, remaining allowance, account status and any roaming setting required by your plan. An operator outage or local restriction can leave voice service available while packet data is unavailable.
Do not repeatedly move the SIM or enter PIN and PUK codes by guess. If the account page shows a suspension or depleted package, resolve that condition with the operator before testing a VPN.
Change APN or DNS only with a way back
Use the APN published by your operator. Photograph or write down the current values before editing them. Random APN lists can break data, tethering or multimedia messaging and may expose traffic to an untrusted intermediary.
A DNS problem can allow an IP connection while domain names fail. Return private DNS to its previous or automatic setting for one test. Changing DNS does not fix missing signal, an unassigned mobile IP or an exhausted data plan.
Use Wi-Fi and another device to narrow the failure
If the phone works on Wi-Fi but not the SIM, focus on the mobile account, APN, coverage and operator. If the same SIM fails in another compatible phone, the evidence points away from one app. If every device in the area fails on the same operator, check official outage information.
Public measurement platforms such as OONI, IODA and Cloudflare Radar can provide broader context, but absence of a public event does not disprove a local cell, account or routing problem.
Try MosVPN only after the base connection carries data
Once ordinary Internet access works, a VPN can test an alternative encrypted route. Connect one configuration, verify the public IP and repeat the same target service. If the whole mobile connection disappears again, disconnect and return to the base-layer checks.
Record the operator, city, time, device, OS and whether Wi-Fi behaves differently. MosVPN cannot restore missing radio coverage or an operator data session, and it cannot guarantee the same outcome across every region.
Follow the MosVPN installation guide for your device and compare one route.
