Unable to send email to multiple recipients in powershell using sendgrid API

I am testing send mail feature in PowerShell using sendgrid API key. The problem is when I give one email in the To list, test email comes successfully but when I add multiple email ids it gives "Cannot convert value to type System.String" error. Can anyone please help :(

function Send-EmailWithSendGrid {
     Param
    (
        [Parameter(Mandatory=$true)]
        [string] $From,

        [Parameter(Mandatory=$true)]
        [String] $To,

        [Parameter(Mandatory=$true)]
        [string] $ApiKey,

        [Parameter(Mandatory=$true)]
        [string] $Subject,

        [Parameter(Mandatory=$true)]
        [string] $Body

    )

    $headers = @{}
    $headers.Add("Authorization","Bearer $apiKey")
    $headers.Add("Content-Type", "application/json")

    $jsonRequest = [ordered]@{
                            personalizations= @(@{to = @(@{email =  "$To"}) 
                                subject = "$SubJect" })
                                from = @{email = "$From"}
                                content = @( @{ type = "text/html"
                                            value = "$Body" }
                                )} | ConvertTo-Json -Depth 10
    Invoke-RestMethod   -Uri "https://api.sendgrid.com/v3/mail/send" -Method Post -Headers $headers -Body $jsonRequest 

}

$MailParams = @{ 
              From = "[email protected]"
                To =  "[email protected]" , "[email protected]"
            APIKEY = "putapikeyhere"
           Subject = "TEST MAIL"
              Body = $HTMLmessage
            }

Send-EmailWithSendGrid @MailParams

I have tried multiple combinations like below but couldn't able to solve this problem.

To = "[email protected]" , "[email protected]"

or

To = "[email protected] , [email protected]"

or

To = " ; "

Error:

Send-EmailWithSendGrid : Cannot process argument transformation on parameter 'To'. Cannot convert value to type System.String.
At line:82 char:24
+ Send-EmailWithSendGrid @MailParams
+                        ~~~~~~~~~~~
    + CategoryInfo          : InvalidData: (:) [Send-EmailWithSendGrid], ParameterBindingArgumentTransformationException
    + FullyQualifiedErrorId : ParameterArgumentTransformationError,Send-EmailWithSendGrid

Not sure if this has already been answered, but I was able to resolve this by using the parameter type as Array and using the FOREACH loop inside the function. (See below).

function Send-EmailWithSendGrid {
     Param
    (
        [Parameter(Mandatory=$true)]
        [string] $From,

        [Parameter(Mandatory=$true)]
        [String[]] $To,

        [Parameter(Mandatory=$true)]
        [string] $ApiKey,

        [Parameter(Mandatory=$true)]
        [string] $Subject,

        [Parameter(Mandatory=$true)]
        [string] $Body

    )

    $headers = @{}
    $headers.Add("Authorization","Bearer $apiKey")
    $headers.Add("Content-Type", "application/json")
    foreach($t in $To){
        $jsonRequest = [ordered]@{
                                personalizations= @(@{to = @(@{email =  "$t"}) 
                                    subject = "$SubJect" })
                                    from = @{email = "$From"}
                                    content = @( @{ type = "text/html"
                                                value = "$Body" }
                                    )} | ConvertTo-Json -Depth 10
        Invoke-RestMethod   -Uri "https://api.sendgrid.com/v3/mail/send" -Method Post -Headers $headers -Body $jsonRequest 
    }
}

$From = "[email protected]"
$To =  @("[email protected]" , "[email protected]")
$APIKEY = "putapikeyhere"
$Subject = "TEST MAIL"
$Body = $HTMLmessage

Send-EmailWithSendGrid -from $From -to $To -ApiKey $APIKEY -Body $Body -Subject $Subject