My internet cannot be activated

Few Carrier (Cellular Service Provider) does not provide Carrier Settings in full but they offer APN settings for example

• Google FI which has APN to be entered manually as h2g2
• MTN Ghana which provides APN pin to be updated manually as the internet
• BSNL in India which provides APN pin to be updated manually as bsnlnet (Watch teh GIF below)

Settings > Mobile Data > APN [under Mobile Data APN] enter the APN pin

View and edit your APN settings

If your carrier allows it, you can view your APN settings in one of the following locations: Settings > Cellular > Cellular Data Options > Cellular Network. Settings> Mobile Data > Mobile Data Options > Mobile Data Network.

View and edit your Access Point Name (APN) on your iPhone ...

Use the APN pin based on your carrier. Ask them (Your Carrrier) or search using any search engine.

If you see No Service or Searching on your iPhone or iPad

1. Check your coverage area. Make sure that you're in an area with cellular network coverage. ... 
2. Restart your iPhone or iPad. Restart your device. ... 
3. Check for a Carrier Settings update. ... 
4. Take out the SIM card. ... 
5. Reset your Network Settings. ... 
6. Update your iPhone or iPad. ... 
7. Contact your carrier. ... 
8. Get more help.

If you see No Service or Searching on your iPhone or iPad ...