You have it in combination with script, I don't know what's wrong.
Without script, this will only get 4 P0.jpg
Code:
[ {
"logging" : true,
"rule" : "DEEPDECRYPT",
"maxDecryptDepth" : 0,
"pattern" : "https?://www\\.depop\\.com/products/[^/]+?/",
"deepPattern" : "url\":\"([^\"]+?P0\\.jpg)\""
} ]