How to do a mail merge with more than 255 Columns

Hello RichardBegg,

I had the same error and searching in Microsoft documentation I found this and based on it, I sent the request in the following way:

{
 "template@odata.bind":"https://graph.microsoft.com/v1.0/teamsTemplates('standard')", 
  "displayName":"My Sample Team",
  "description":"My Sample Team’s Description", 
  "members":[ 
     { 
       "@odata.type":"#microsoft.graph.aadUserConversationMember",
       "roles":[ "owner" ], 
       "user@odata.bind":"https://graph.microsoft.com/v1.0/users('0040b377-61d8-43db-94f5-81374122dc7e')" 
      }
   ] 
}

The request was success.