Hi
The custody petition has to be on the bais of the facts stated in the divorce petition and in the terms and conditions what you agreed .
If there was a term you agreed that permanent custody of your daughter will be with your husband now you you need to prove a reason why you are asking for the custody.
You being the biological mother is the natural guardian , you can get the custody of your daughter , fight for it in the court.
The whats Aapp messages may or may not be brought in the court. in a divorce matter this can be used as an emotional cruelty against the spouse, but in custody matter the message will not prove that you are continuing the relationship.
This will not be an impediment for the custody.
Your husband has to prove that you are not a fitting parent.
since he is not earning is a good reason for you to ask custody and mention that your daughter is not happy and not kept well by him and his family.
you consult a lawyer with your divorce papers and the decree copy. whether you get the custody or not please try for it as your daughter will be better brought up with her mother.