Although everything is decided by Hashem and we trust that he gives us all that we need, we must still ask for things, if we want Hashem to send them. That is why the Chachomim made a Bracha in Shmoneh Esrei for Parnassa. To what degree of specificity may a person daven? Do we have a right to request from Hashem to send it through a specific means, or must we just ask him to support us financially and leave it purely to his discretion via which channels He’d like to send it?
RavYisroel Yaakov Fisher (Even Yisroel 9:61:21) says that indeed you may not petition Hashem as to how, or through which opportunity, Hashem should provide you with a livelihood. Your request should be limited to asking for a comfortable income. However say Rav Fisher, that is before you start working on a particular venture. Once you are already involved in it and this is your Hishtadlus, you may daven for its success. Revach.