How to check if output from command contains "error"? - powershell

Question

I have 2 powershell scripts
script1.ps1 contains REST calls to Vault, which returns a json response containing some keys/values.
Function getValues($token) {
$headers = New-Object "System.Collections.Generic.Dictionary[[String],[String]]"
$headers.Add("X-Vault-Token", $token)
$response = Invoke-RestMethod -method GET -uri "https://vault.com:8243/v1/secret/vault/development" -ContentType 'application/json' -headers $headers
$response.data| ConvertTo-Json -depth 100
}
getValues $token
As you can see, the method requires a $token.
I have that token saved in a system variable.
Now i call script1 in script2 to get the keys/values like this:
$resp = & ".\script1.ps1" | convertfrom-json
that works great and i get values as i need.
however, i am testing when if there is errors in the future, for example by removing the token from the system variable.
This $resp returned:
errors
------
{missing client token}
great. now i want to exit the script should that happen.
I tried a check like this:
if($resp.tostring().contains("error"))
{
write-output "error!"
exit 1
}
but it never exited nor did it return the output error!
how am i suppose to look for a match in this case?