TS100-C4 Soldering Iron Tips, Rapid Heating Replacement Solder Tips Compatible with TS100, TS101, Pine64 and Pinecil Soldering Irons -Accurate Soldering Easy to Install

If you can afford it I highly recommend getting a TS100 soldering iron (or similar style) and getting a bevel tip for it like this. It helps so much as a beginner to be able to press the flat tip against the motor wire and have the solder flow evenly across the entire wire. You can also improvise straps, if you have any wire bundling velcro you can connect two if one is big enough to make it all the way around. Worst case you can use zip ties as a temporary solution, just put a piece of cardboard under the part where the zip tie tightens. It's also very easy to order larger size straps from an FPV retailer. Your receiver probably either has two wires bridged together or the other strong possibility is that you have the TX/RX wires mixed up. Feel free to swap them and try again, it doesn't cause any permanent damage and I find flight controller diagrams and labeling is often wrong. Also if all else fails, make sure your stack screws are not tightened down too much it's possible to compress the FC and ESC so much they either short or something cracks.