What does "invalid account discriminator" mean in Anchor?

An account discriminator is few bytes that Anchor puts at the front of an account, like a header. It lets anchor know what type of account it should deserialize the data as.

This error happens if you try to to fetch something as myAccountType, but it's actually a pubkey for some other account, like a Token Account, or another account within your program.

Here's some things you could try:

• console logging somePubkey and putting it into the explorer
• making extra double sure that you meant program.account.myAccountType and not program.account.someOtherAccountType.

In my case this problem occurred after I did anchor idl init [OPTIONS] --filepath <FILEPATH> <PROGRAM_ID>.

Once I ran this command the frontend started to throw Error: Invalid account discriminator every time I tried to run await connection.getProgramAccounts().

I wanted to do the anchor idl init because I wanted to fetch the idl using Program.fetchIdl() instead of passing idl as a json object, which requires me to copy it from target/idl/<program-name>.json into my React frontend and then import the json into my project...

To fix the issue I had to rebuild and redeploy anchor program by running anchor build and then anchor deploy. Once I did this then I had to pass the idl as a json object into the Program.getProgramAccounts() function.

I had the same error come up when I had put my accounts in the wrong order. As a result the discriminator didn't match up with what it expected.