Red eyed tree frog breeding problems

[falex]

hi all, i've recently got 3 RETFs, the seller said that there were 2males and 1female within those three, and he claims that they're adults. i placed them into a rain chamber and through these few days i've notice that there are calls at the midnight but only happens once a time per few mins, so im just wondering if i should consider it as mating call, cuz i know that it should happen once per few secs. till now, still they are not showing any signs of mating at all, which the 2 males and the female didnt have any interactions, just sometimes staring at each others.
so anyone can tell me wt's going on, or what should i do to rise up the willingness of them to mate? i've tried playing the mating call of retf from the internet, but it seems like they arent responding significantly. thanku all.
btw, sry for the poor english usage, cuz im from hk lol.