Q: No sim installed error

Did you already check the troubleshooting?

If you see 'No SIM' alert on iPhone - Apple Support

Has the phone been officially unlocked by the provider?

iPhone: About unlocking

As long as you did not get the info that the phone has been unlocked, any other SIM will not be recognized.

Click on the blue link above to find out what to do if you get that info, part of which will be using iTunes to restore the phone.

Follow these steps to set your phone back to factory settings and restore from the latest backup afterwards.

Without restoring you will not be able to use your phone, because iTunes will not look it up in the database of phones to be unlocked.

1. After your carrier confirms that your iPhone unlock has been processed, go to the next section.

If you have a SIM card from a carrier other than your current carrier, follow these steps:

1. Remove your SIM card and insert the new SIM card.
2. Complete the setup process.

If you don't have another SIM card you can use, follow these steps to complete the process:

1. Back up your iPhone.
2. When you have a backup, erase your iPhone.
3. Restore your iPhone from the backup you just made.

Get help

Follow these steps if you have any issues or if you see this message in iTunes or on your device:"The SIM card inserted in this iPhone does not appear to be supported. Only compatible SIM cards from a supported carrier may be used to activate iPhone. Please insert the SIM card that came with your iPhone or visit a supported carrier store."

1. Restore your iPhone to factory settings.
2. Contact your carrier to verify that the unlock was applied in your carrier's system.
3. Restore your iPhone from a backup.

Glad that restoring the device unlocked the phone for the use with another provider