Can't access object property from inside nested loop - powershell

Question

Below is my code, I have tried making the object a global variable as well but that doesn't seem to help. Doing += syntax gives the same error as .add() syntax.
foreach ($x in $groups_data) {
$group_name = $x.targetName
$group_shifts_path = "$base/api/xm/1/groups/$group_name/shifts"
$group_shifts_req = Invoke-WebRequest -Credential $cred -Uri $group_shifts_path
$group_shifts_res = ConvertFrom-Json $group_shifts_req.Content
$group_shifts_data = $group_shifts_res.data
foreach ($y in $group_shifts_data) {
$shift_name = $y.name
$shift_id = $y.id
$group_info = #{
'group_name' = $group_name
'offending_shifts' = #{}
}
$group_info = $group_info | ConvertTo-Json
$group_shift_members_path = "$group_shifts_path/$shift_id/members"
$group_shift_members_req = Invoke-WebRequest -Credential $cred -Uri $group_shift_members_path
$group_shift_members_res = ConvertFrom-Json $group_shift_members_req.Content
$group_shift_members_data = $group_shift_members_res.data
foreach ($z in $group_shift_members_data) {
if ($z.recipient.recipientType -ne 'PERSON') {
$group_info.offending_shifts += $shift_name # HERE'S MY ISSUE
break
}
}
}
}
There error I am getting is the following:
The property 'offending_shifts' cannot be found on this object. Verify that the
property exists and can be set.
At \\etoprod\xMatters\PowerShell Scripts\Group Shift Cleanup & Notify.ps1:42 char:17
+ $group_info.offending_shifts += $shift_name
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidOperation: (:) [], RuntimeException
+ FullyQualifiedErrorId : PropertyAssignmentException
Why can't I access this property?