Проблема не в JSON, чего-то вы не то делаете, о чем говорите, всё отлично работает:
var_dump(json_decode('{"1337":{"Id":"20824","Url":"/coins/1337/overview","ImageUrl":"/media/350976/1337.png","Name":"1337","CoinName":"1337","FullName":"1337 (1337)","Algorithm":"X13","ProofType":"PoW/PoS","FullyPremined":"0","TotalCoinSupply":"314159265359","PreMinedValue":"2353115.7216","TotalCoinsFreeFloat":"N/A","SortOrder":"577"}}'));
class stdClass#2 (1) {
public $1337 =>
class stdClass#1 (13) {
public $Id =>
string(5) "20824"
public $Url =>
string(20) "/coins/1337/overview"
public $ImageUrl =>
string(22) "/media/350976/1337.png"
public $Name =>
string(4) "1337"
public $CoinName =>
string(4) "1337"
public $FullName =>
string(11) "1337 (1337)"
public $Algorithm =>
string(3) "X13"
public $ProofType =>
string(7) "PoW/PoS"
public $FullyPremined =>
string(1) "0"
public $TotalCoinSupply =>
string(12) "314159265359"
public $PreMinedValue =>
string(12) "2353115.7216"
public $TotalCoinsFreeFloat =>
string(3) "N/A"
public $SortOrder =>
string(3) "577"
}
}
var_dump(json_decode('{"1337":{"Id":"20824","Url":"/coins/1337/overview","ImageUrl":"/media/350976/1337.png","Name":"1337","CoinName":"1337","FullName":"1337 (1337)","Algorithm":"X13","ProofType":"PoW/PoS","FullyPremined":"0","TotalCoinSupply":"314159265359","PreMinedValue":"2353115.7216","TotalCoinsFreeFloat":"N/A","SortOrder":"577"}}', true));
array(1) {
[1337] =>
array(13) {
'Id' =>
string(5) "20824"
'Url' =>
string(20) "/coins/1337/overview"
'ImageUrl' =>
string(22) "/media/350976/1337.png"
'Name' =>
string(4) "1337"
'CoinName' =>
string(4) "1337"
'FullName' =>
string(11) "1337 (1337)"
'Algorithm' =>
string(3) "X13"
'ProofType' =>
string(7) "PoW/PoS"
'FullyPremined' =>
string(1) "0"
'TotalCoinSupply' =>
string(12) "314159265359"
'PreMinedValue' =>
string(12) "2353115.7216"
'TotalCoinsFreeFloat' =>
string(3) "N/A"
'SortOrder' =>
string(3) "577"
}
}