Croaking frogs indicates the males are present and maturing; not that there are females (grow bigger and will lack nuptial pads) in there.

For breeding, it's recommended to time it with their natural breeding cycle from May to November. You need to group house them with 3 males per 2 females ratio. To condition frogs, first lower humidity around 30-50% to simulate a dry season and feed them well for couple months. Then follow it up with a heavy rainy season simulated inside a rain chamber. Timing rain chamber with it a local storm (atmospheric pressure front) will help trigger breeding. Good luck !