sim card won't register

It would be helpful if you told us the make and model of the handset you're trying to use with the iD Mobile SIM @Roo Stuart. Also, where did you get it from? Is it network unlocked?

It's an Oppo phone, the ID SIM card has been working fine for the last month but tonight it has decided to stop working. It works in other phones and other SIM cards work in my phone. There's a message that says " disable esim to use sim" 

OK, your phone is telling you what the problem is and how to resolve it @Roo Stuart. You need to delete or disable the eSIM profile you setup and activated.

How do I do that? 

A quick Google shows the following:

How to Uninstall an eSIM from Oppo Device

1. Go into Settings.
2. Go into "Mobile network"
3. Click into "eSIM".
4. Select the eSIM you want to remove (for this example, we are using "Data eSIM").
5. Click on the 3 dots shown on the right hand side and select "Delete".