Prometrium instead of Utrogestan for FET?

I'm in Australia starting a frozen embryo transfer and was told to begin Utrogestan three times daily vaginally from tomorrow morning, but I wasn't given a prescription and don't have it yet. I do have Prometrium on hand, but the nurses said they don't usually use it vaginally during an FET. Has anyone bridged with Prometrium until they got Utrogestan, or did you have to delay? Following up with an urgent care dr too just keen to hear how others handled it.