Hey SHWs and FCs! If I had any way to tell you this without sounding #snarkyaf, I promise I would! I have answered this question so many times and in so many ways...
There are 2 types of vinyl that we all MAINLY use in the everyday hustle/craft. We use Heat Transfer Vinyl (HTV) and Sticker/Decal 651 grade adhesive vinyl. As the name implies, one is a sticker. The other is designed for use with heat to adhere it to a surface.
Now consider the surface you are trying to put the vinyl on and ask yourself, would a sticker work on this surface for long term (up to 5 years under ideal conditions)? If the answer is NO, ask yourself, "Self, does this item require me to use a source of heat to adhere vinyl to this item because neither item is already sticky?..." then you should be using HTV.
More to consider is that if you are not ready to make this distinction, perhaps you are not where you need to be in your research and testing. It is advisable NOT TO ACCEPT AN ORDER/HUSTLE until you are knowledgeable enough about the products and process. Your reputation as an artist, designer, hustler will be tarnished before you get a second order. Crawl, walk, run.
We (professionals) cannot think it, do it, or understand it for you. It is your hustle. You accepted it. You implied that you were professional enough and knew your craft well enough to take the job. Now you have a decision to make. Return the money or figure it out for yourself. Good luck in your Hustle!
Respectfully, and you're welcome. - Amanda