Looping an invoke-RestMethod? - powershell

Question

So I'm trying to automate a process at work which involves hitting SendGrid's API. For a short explanation.. with SendGrid you have Subusers and underneath those Teammates. There is no ready option to search all teammates, so you have to supply a subuser then display all teammates underneath. Rinse, repeat down the line. Well I'd like to automated as best as I can.
So the idea is to collect a teammate email address from then user then dump into a variable all the subusers then loop through those subusers looking for the $email variable.
I've never actually used loops in my scripts over the years so it's new territory for me and combining it with an invoke-restmethod just boggles me. heres what Ive got so far:
$token = 'xxxxxxxxxxxxxxxxxxx'
#First uri is to pull a list of subusers
$uri = "https://api.sendgrid.com/v3/subusers"
#Prompts for target email address
$email = Read-Host "Enter the users email"
$headers1 = #{"Authorization" = "Bearer $token"}
$headers2 = #{"Authorization" = "Bearer $token"
"on-behalf-of" = "$subuser"
}
$subs = Invoke-RestMethod -Method get -uri $uri -headers $headers1
$subarray = $subs | select-object username
foreach ($su in $subarray){
$teamarray = invoke-restmethod -method get -uri "https://api.sendgrid.com/v3/teammates?limit=500&offset=0" -headers $headers2
#$teamarray.gettype()
}
The last line is commented out.. i was trying to find teh type of the $teamarray data but it's giving this error for each loop through the subusers:
invoke-restmethod : {"errors":[{"field":null,"message":"authorization required"}]}
At line:18 char:18
+ ... teamarray = invoke-restmethod -method get -uri "https://api.sendgrid. ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidOperation: (System.Net.HttpWebRequest:HttpWebRequest) [Invoke-RestMethod],
WebException
+ FullyQualifiedErrorId : WebCmdletWebResponseException,Microsoft.PowerShell.Commands.InvokeRestMethodComma
nd
This should mean the invoke-restmethod is malformed somehow. Any pointers would be appreciated!