That is the BBCode format, just remove the spaces "[ _spoiler_ ]" spoiler content "[ _/spoiler_ ]", I had to add them otherwise the forum would convert them to spoiler tags (codebox doesn't work on them somehow)
Also you can use the sixth icon from the left, it has the spoiler tag in there
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[ img]https://us.v-cdn.net/5019629/uploads/userpics/710/nQ2K7UN7RKXRE.jpg[/img]
[/ spoiler ]
That is the BBCode format, just remove the spaces "[ _spoiler_ ]" spoiler content "[ _/spoiler_ ]", I had to add them otherwise the forum would convert them to spoiler tags (codebox doesn't work on them somehow)
Also you can use the sixth icon from the left, it has the spoiler tag in there