Is that the amazon stuff for $11 with “free” shipping? Oof. I bought solder like that once, and never again. Buy yourself some name brand like Kester, MG Chemicals, etc (I use the latter) in 63/37 since it turns instantly from fluid to solid (60/40 has a semi-solid state that if moved will make cold joint) and you’ll be fine. You’ll probably need some additional flux too