As an additional point to this, it would be advisable that the match cannot be played until the following day, at the earliest, after agreement is made by the recipient of the request. Likewise I logged in today 5 mins before a league match to see my team had played a friendly without me knowing. It threw my team plans out as I had a CL match later that day. If the friendly could not be played until the day after I had given approval, at least then I could plan appropriately