One possibility is that your APN settings haven't been set up.
Apple Guide
Apple Guide
Tap on Cellular (or Mobile Data).
Tap on Cellular Data Options (or Mobile Data Options).
Tap on Access Point Name (APN) under Cellular Data Network.
Then, ensure that it says "wholesale" next to APN under Personal Hotspot. If it doesn’t, you can edit it accordingly.
Save the changes, and your hotspot should work. Let me know if this works for you!
Android Guide
Android Guide
Open the Access Point Names or APNs menu.
In Settings, check under Wireless & Networks or choose the Connections tab.
Select Mobile network. You may need to choose More settings, More..., or More networks first.
Select Access Point Names.
Choose the existing APN if one is available and confirm if the APN is set to 'wholesale'. If not, select Menu and select new APN.
Verify and update the following settings for the Data APN.
Name: Panda Mobile (or anything you want)
APN: wholesale
Proxy: <Not set>
Port: <Not set>
Username: <Not set>
Password: <Not set>
Server: <Not set>
MMSC: http://wholesale.mmsmvno.com/mms/wapenc
MMS proxy: <Not set>
MMS port: <Not set>
MMS protocol: WAP 2.0
MCC: 310
MNC: 260
Authentication Type: <Not set>
APN Type: default,mms,supl,dun
Note: If it doesn't let you type "dun", try typing default,mms,supl first, save it, and then go back in to add ,dun.
APN Protocol: IPv4/IPv6
APN roaming protocol: IPv4/IPv6 or IPv4 only when roaming internationally
Turn APN on/off: Grayed out unless there are multiple APNs
Bearer: Unspecified
Tap the three dots (top right) > Save.
Select this new APN (radio button turns blue).
Toggle Airplane Mode on for 10 seconds, then off. Try the hotspot again.