Prayer plant going downhill

[Marb67]

Well I just don't know why this once thriving plant has taken a decline as it just doesn't want to live. I have it in a warm spot, let the soil dry before watering (as advised) but it just looks pathetic.

Can anyone help me rescue yet another dying plant ?

Thanks

[Snoop Puss]

I've never had one, Marb, so not an expert. They look very pretty. Might the cultivation section of this website help? I notice no direct sunlight and minimum of 15 ºC at night. Might be a bit chillier than that if it's behind a curtain at night.
https://en.wikipedia.org/wiki/Maranta_leuconeura